Mercury and Carbon in Marine Pelagic Zooplankton: Linkage with Oceanographic Processes in the Canadian High Arctic.
By Corinne Pomerleau
A Thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in partial fulfilment of the requirements of the degree of
MASTER OF SCIENCE
Department of Environment and Geography University of Manitoba Winnipeg, Manitoba
Copyright © 2008 Corinne Pomerleau Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition
395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada
Your file Votre reference ISBN: 978-0-494-49054-9 Our file Notre reference ISBN: 978-0-494-49054-9
NOTICE: AVIS: The author has granted a non L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats.
The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission.
In compliance with the Canadian Conformement a la loi canadienne Privacy Act some supporting sur la protection de la vie privee, forms may have been removed quelques formulaires secondaires from this thesis. ont ete enleves de cette these.
While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. Canada THE UNIVERSITY OF MANITOBA
FACULTY OF GRADUATE STUDIES
COPYRIGHT PERMISSION
Mercury and Carbon in Marine Pelagic Zooplankton: Linkage with Oceanographic Processes in the Canadian High Arctic.
BY
Corinne Pomerleau
A Thesis/Practicum submitted to the Faculty of Graduate Studies of The University of
Manitoba in partial fulfillment of the requirement of the degree
Of
MASTER OF SCIENCE
Corinne Pomerleau © 2008
Permission has been granted to the University of Manitoba Libraries to lend a copy of this thesis/practicum, to Library and Archives Canada (LAC) to lend a copy of this thesis/practicum, and to LAC's agent (UMI/ProQuest) to microfilm, sell copies and to publish an abstract of this thesis/practicum.
This reproduction or copy of this thesis has been made available by authority of the copyright owner solely for the purpose of private study and research, and may only be reproduced and copied as permitted by copyright laws or with express written authorization from the copyright owner. Abstract
This thesis investigates the relationships between mercury (Hg) and stable isotope of carbon (513C) in marine pelagic zooplankton (Calanus spp., Themisto spp. and Euchaeta spp.) with water mass characteristics in the North Water Polynya (NOW) and in the
Mackenzie shelf - Amundsen Gulf area. Two ship based sampling field expeditions were carried out in late summer of 2005 and 2006 in both regions on board the CCGS
Amundsen.
In the North Water (NOW) polynya, higher levels of water Hg, depleted 8180, lower salinity and lower nitrate levels were measured at sampling locations near the Prince of
Wales glacier (POW) on the eastern coast of Ellesmere Island in the Smith Sound area.
These results suggest that the glacier may be a source of Hg to this region which, in turn, is responsible for the correspondingly high concentrations of THg and MMHg measured in
Calanus spp. and Euchaeta spp. at the same locations.
The Mackenzie shelf - Amundsen Gulf region was characterized by fresher surface water properties (low salinity and depleted 5180) in the western part and was strongly linked to influence of the Mackenzie River. Higher THg concentrations in zooplankton were associated with larger fractions of both meteoric water and sea-ice melt. These findings suggest that in the western Arctic, inorganic Hg uptake in zooplankton via-absorption near surface water was highly driven by freshwater inputs into the system.
ii Based on the analysis of three main genus Calanus spp. (mostly adult females Calanus hyperboreus), Euchaeta spp. and Themisto spp. (mostly adult Themisto libellula), THg and
MMHg concentrations were the highest in the carnivorous copepod Euchaeta spp. in the
North Water polynya followed by the omnivorous hyperiid amphipod Themisto spp. The herbivorous copepod Calanus spp. had both the lowest THg and MMHg concentrations in the Eastern and the Western Arctic. In addition, the Western Arctic is the area in which each zooplankton genus had the most depleted carbon and the most enriched nitrogen. The highest concentrations of THg in Calanus spp., Euchaeta spp. and Themisto spp. were measured in the Western Arctic as well as the highest MMHg in Calanus spp. and
Themisto spp. The highest %MMHg was calculated in the Archipelago for Themisto spp., in the Eastern Arctic for Euchaeta spp. and in the Western Arctic for Calanus spp.
The relationships observed between THg, MMHg, %MMHg and 513C in all three major zooplankton taxa and water mass properties were in agreement with what have been previously described in the literature. Our findings suggested that both Hg and 813C can be used as tracers to help understand zooplankton vertical distribution, feeding ecology and ultimately to predict climate changes impact at lower trophic level in the pelagic food web.
The implications for marine mammals foraging in these regions are also discussed.
in Acknowledgements
I would like to thank my thesis supervisor, Dr. Gary Stern, for all his support and guidance all the way through the length of this project. I would also like to thank Dr. Steve Ferguson and Dr. Feiyue Wang for being on my committee. Special thanks to our contaminant team
Joanne DeLaronde, Gail Boila, Debbie Armstrong, Bruno Rosenberg, Allison Machutchon and Jesse Carrie for their help in the lab and/or in the field. I am grateful to the Captain and crews of the Canadian Coast Guard Ice Breaker Amundsen during the Leg 1 of 2005 and
2006. I also want to give a special thank you to Louis Fortier team and especially to Louis
Letourneau for his help in the field with zooplankton collection. Special thanks to Jean-Eric
Tremblay and his team for providing nutrients data. Many thanks to Dr. Robie Macdonald for his help and advice during this project. I am also grateful for all the support from my friends and particularly my parents, Celine Parent and Yvan Pomerleau. Financial support was provided by ArcticNet, the Department of Fisheries and Oceans Canada (DFO) and the
Northern Scientific Training Program (NSTP).
IV Dedication
To my parents and especially my mother who truly help me all along the process of this thesis by giving me an endless support and motivated me to keep me going until the end.
v Table of Contents
Abstract ii Acknowledgments iv Dedication v List of Tables viii List of Figures xi List of Copyrighted Material for which Permission was Obtained xv
Chapter 1 - Introduction 1 References 5
Chapter 2 - Linkage between Mercury and Oceanographic Processes in Marine Pelagic Zooplankton in the North Water Polynya, August and September 2005- 2006 6 Abstract 7 Introduction 8 Materials and Methods 12 Water collection and analysis 12 Zooplankton collection analysis 15 Statistical Analysis 17 Results and Discussion 18 Water masses structure in the North Water polynya and linkages with mercury concentration in sea water 18 THg water concentration and profiles 37 Prince of Wales subglacial runoff as a source of mercury to the NOW polynya 39 Mercury levels and stable isotopes in zooplankton 44 Linkages between biological and physical processes 46 Calanus spp 48 Euchaeta spp 50 Themisto spp 52
vi Biomagnification factors (BMF's) 53 Implications to marine mammals 56 References 59
Chapter 3 - Relationships between Mercury, 813C and Water Masses in Marine Pelagic Zooplankton of the Mackenzie Shelf-Beaufort Sea, in September and October 2005-2006 63 Abstract 64 Introduction 65 Materials and Methods 68 Water collection analysis 69 Zooplankton collection and analysis 71 Statistical analysis 72 Results and Discussion 73 Mercury levels in zooplankton 73 Carbon and nitrogen in zooplankton 78 Hydrography 83 THg water concentrations and profiles 103 Linkages between biological and physical processes 104 Calanus spp 108 Themisto spp 109 Euchaeta spp 113 Biomagnification factors (BMF's) 116 Implications to marine mammals 119 References 124
Chapter 4 - Conclusion 128
vii List of Tables
Chapter 2
Table 1. Summary table of salinity, 8180, temperature, THg levels, nitrate, phosphate
and chlorophyll a maximum at surface, 25, 50, 100 and 200 meters at each
of the 8 stations (mean± SE) in the North Water Polynya 21
Table 2. Total mercury (THg), methyl mercury (MMHg) and percent methyl mercury
in THg (%MMHg), 813C and 815N values for Calamus spp., Euchaeta spp.
and Themisto spp. at the 8 sampling sites (mean ± SE) in the North Water
Polynya 45
Table 3. Significant interactions between THg, MMHg, %MMHg of THg and 813C in
Calanus spp., Euchaeta spp. and Themisto spp. with salinity, 8180,
temperature and percent Pacific water in the North Water Polynya. Dep.
Var. is the dependant variable, r2 is the correlation coefficient and p is the
level of significance of the test 51
Chapter 3
Table 1. Total mercury (THg), methyl mercury (MMHg) and percent methyl mercury
in THg (%MMHg), 813C and S15N values for Calanus spp., Euchaeta spp.
and Themisto spp. at the 10 sampling stations on the Mackenzie Shelf-
Beaufort Sea region (mean ± SE) 74
Table 2. Results from a) ANCOVA on longitudinal gradient and b) ANCOVA on
latitudinal gradient in 813C among the 4 most ubiquitous genus {Calanus
vni spp., Euchaeta spp., Sagitta spp. and Themisto spp.) on the Mackenzie
Shelf-Beaufort Sea region 79
Table 3. Summary table of salinity, 5180, temperature, THg levels, nitrite, nitrate,
phosphate and silicate at surface, 25, 50,100 and 200 meters at each of the 9
stations (mean ± SE) on the Mackenzie Shelf-Beaufort Sea region 85
Table 4. Summary table of the significant interactions between THg, MMHg,
%MMHg of THg. and 513C in Calanus spp., Euchaeta spp. and Themisto
spp. with salinity, 8180, temperature, percent Pacific water, fraction of
meteoric water (FMW) and fraction of sea ice melt (FSIM) on the
Mackenzie Shelf-Beaufort Sea region. Dep. Var. is the dependant variable,
r2 is the correlation coefficient and p is the level of significance of the test 110
Table 5. Summary table of the fraction of meteoric water (FMW), fraction of sea ice
melt water (FSIM), fraction of salty Atlantic water (FPML) and percent
Pacific water at surface, 25, 50, 100 and 200 m at each of the 9 stations on
the Mackenzie Shelf-Beaufort Sea region Ill
Table 6. Methyl mercury (MMHg) biomagniflcation factors (BMFs) in different areas
of the Canadian Arctic 118
Chapter 4
Table 1. Vertical distribution in the NOW Polynya and in the Western Arctic as
suggested from the data in this study and what has been described in the
literature in other areas of the Arctic for Calanus spp., Euchaeta spp. and
Themisto spp 133
ix Table 2. Stable isotopes of carbon and nitrogen (8 C and 8 N), total mercury (THg),
methyl mercury (MMHg) and percent methyl mercury in THg (%MMHg) in
various genus from the Eastern Arctic, the Arctic Archipelago and the
Western Arctic 134
x List of Figures
Chapter 2
Figure 1. Sampling locations in the North Water Polynya (NOW). Red circles
represent stations where zooplankton were collected, red circles with a green
border represent Hg water collection stations and the black dots represent the
CTD stations 13
Figure 2. Schematic cross-section pf ocean circulation beneath the NOW region.
Circled crosses and dots indicate current directed into and out of the plane
figure, respectively. Small arrows represent the circulation in the vertical
plane 19
Figure 3. NOW Polynya transects A: 127 to 131, B: 118 to 126, C: 101 to 115 and D:
132-127-118-101 20
Figure 4. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio
contour plots for the sampling transect 1 of the North Water Polynya. Water
THg concentrations are superimposed onto each of the 5 contour maps for
station 127 23
Figure 5. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio
contour plots for the sampling transect 2 of the North Water Polynya. Water
THg concentrations are superimposed onto each of the 5 contour maps for
station 118 27
Figure 6. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio
contour plots for the sampling transect 3 of the North Water Polynya. Water
XI THg concentrations are superimposed onto each of the 5 contour maps for
stations 101,108 and 115 31
Figure 7. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio
contour plots for the sampling transect 4 of the North Water Polynya. Water
THg concentrations are superimposed onto each of the 5 contour maps for
stations 127, 118 and 101 34
Figure 8. Principal Component Analysis (PCA) results, a) Factors loading plot and b)
Score plot for data measured in the North Water Polynya, 2005 and 2006 38
Figure 9. Spatial trends of abiotic variables measured at surface, 25, 50, 100 and 200
meters, a) salinity, b) 8180, c) temperature, d) nitrate levels, e) chlorophyll a
max values and chlorophyll max depths and f) THg levels in water from the
North Water Polynya 40
Figure 10. Relationships between THg levels in water and a) THg in Calanus spp., b)
THg in Euchaeta spp., c) MMHg in Calanus spp. and d) MMHg in
Euchaeta spp. from the North Water Polynya 43
Figure 11. Biomagnification factors (BMFs) in the North Water Polynya. Dark grey
bars represent BMF between Themisto spp. and Calanus spp. and light grey
bars represent BMF between Euchaeta spp. and Calanus spp 55
Chapter 3
Figure 1. Sampling locations on the Mackenzie Shelf-Beaufort Sea region. Red
circles represent stations where zooplankton were collected, red circles with a
xii green border represent Hg water collection stations and the black dots
represent the CTD stations 70
Figure 2. Spatial patterns of a) THg in Calanus spp., b) THg in Themisto spp., c) THg
in Euchaeta spp, d) MMHg in Calanus spp., e) MMHg in Themisto spp. and
f) MMHg in Euchaeta spp. on the Mackenzie Shelf-Beaufort Sea region 76
Figure 3. Spatial patterns of a) %MMHg in THg in Calanus spp., b) %MMHg in THg
in Themisto spp., c) %MMHg in THg in Euchaeta spp, d) Salinity 0-10m, e)
5180 0-10m and f) Fraction of meteoric water (FMW) 0-10m on the
Mackenzie Shelf-Beaufort Sea region 77
Figure 4. Mean 8 C values ± SE of all zooplankton genus pooled at each station
(n=14) against longitude across the Mackenzie Shelf-Beaufort Sea region 80
Figure 5. Relationships between 513C and 815N for zooplankton across the Mackenzie
Shelf-Beaufort Sea region 82
Figure 6. Mackenzie Shelf-Eastern Beaufort Sea transects: 1: 421-434, 2: 410-420, 3:
403-408. Red star represents station 436 in Franklin Bay 84
Figure 7. a) temperature, b) temperature in surface layer, c) salinity, d) salinity in
surface layer, e) nitrite, f) nitrate, g) phosphate, h) silicate and i) N:P ratio
contour plots for the sampling transect 1 on the Mackenzie Shelf-Beaufort
Sea region. Water THg concentrations are superimposed onto each of the 9
contour maps for station 435 87
Figure 8. a) temperature, b) salinity, c) nitrite, d) nitrate, e) phosphate, f) silicate and
g) N:P ratio contour plots for the sampling transect 2 on the Mackenzie
xm Shelf-Beaufort Sea region. Water THg concentrations are superimposed
onto each of the 7 contour maps for station 420 94
Figure 9. a) temperature, b) salinity, c) nitrite, d) nitrate, e) phosphate, f) silicate and
g) N:P ratio contour plots for the sampling transect 3 on the Mackenzie
Shelf-Beaufort Sea region. Water THg concentrations are superimposed
onto each of the 7 contour maps for station 420, 407, 405 and 403 99
Figure 10. Principal Component Analysis (PCA) results, a) Factors loading plot and
b) Score plot for data derived from the Mackenzie Shelf-Beaufort Sea
region 105
Figure 11. Spatial trends of a) salinity at surface, 2.5, 5, 7.5 m, b) 8180 at surface, 2.5,
5, 7.5 m and c) THg levels in Calanus spp., Euchaeta spp. and Themisto
spp. on the Mackenzie Shelf-Beaufort Sea region 106
Figure 12. MMHg Biomagnification factors (BMFs) for the Mackenzie Shelf-
Beaufort Sea region. Dark grey bars represent BMF between Themisto spp.
and Calanus spp. and light grey bars represent BMF between Euchaeta spp.
and Calanus spp 117
xiv List of Copyrighted Material for which Permission was Obtained
Schematic cross-section of ocean circulation beneath the NOW region. Circled crosses and dots indicate current directed into and out of the plane of the figure, respectively. Small arrows represent the circulation in the vertical plane.
Ocean Circulation within the North Water Polynya of Baffin Bay by Humfrey Melling,
Yves Gratton and Grant Ingram, ATMOSPHERE-OCEAN, 2001, Vol. 39, Issue 3, p. 320
(Fig.13).
Chapter 2, Page 19.
xv Chapter 1 - Introduction
The whole planet is now facing the greatest challenge of human history, a phenomena known as global warming. While all over the globe humans are facing numerous natural catastrophes and are threatened by inundations, destructive storms, land erosion, forest fire and rising sea levels, the strongest impacts and changes are occurring at the poles (1,2).
Throughout the last few decades, the Arctic average air temperature has risen at nearly twice the rate as the rest of the planet (3). Climate change in the Arctic is causing the ice to melt earlier and faster allowing a greater surface of the ocean to receive heat from the sunlight causing the acceleration in the ice melting rate (4). In September 2007, the Arctic sea ice extent reached a new and unprecedented record low of 4 millions km2. The IPCC
(Intergovernmental Panel of Climate Change) climate scenario is now calling for a disappearance of the summer arctic sea ice cover by 2050 (5).
Recent studies strongly suggest that a warmer Arctic will enhance loading of contaminants, such as mercury (Hg), into the marine system from melting permafrost and river inputs as well as long range atmospheric transport and ocean currents (3,6). The Canadian High
Arctic is composed of different water masses that form along ocean circulation through the interaction of currents, fronts and sea ice processes. The main flow of water moves from west to east through the Archipelago linking the Pacific and the Atlantic Oceans through surface outflow of the Arctic Ocean water to the North Atlantic and the rest of the World
Oceans (7). Hg loading to the Arctic marine area affects every trophic level from particulate organic matter all the way through to marine mammals and ultimately humans
1 as Inuit traditional diet comprises an important part of Arctic marine food web components
(8). The role of zooplankton in contaminant transfer and energy flux in the Arctic pelagic food web is crucial, since zooplankton is in the first steps of the marine food chain and thus is direct food for many species offish, birds and marine mammals (9-11).
Hg is regarded as one of the most important contaminants of concern in the Arctic. Mono- methylmercury (MMHg) is a potent neurotoxin that bioaccumulates through marine food webs where it can reach substantial levels in top predators such as beluga (Delphinapterus leucas), ringed seal (Phoca hispida) and polar bears {Ursus maritimus) (12).
Bioaccumulation is a general term for the accumulation of a substance such as MMHg in an organism or part of an organism over time (12). Beaufort belugas are of particular interest with respect to Hg, as this population has seen the greatest concentration of Hg. In fact, liver Hg levels in that beluga whale population tripled in the 1990s compared to levels in the 1980s although recent measurement suggest a small decline (13).
Within-ecosystem processes are thought to play a critical role in the toxicity and distribution of Hg in the Arctic (14). For example, riverine Hg discharge, direct terrestrial
Hg input from melted permafrost and coastal erosion, oceanic Hg transport (15), sea ice
loss, marine mammal habitats, feeding patterns and food web structures (16) are thought to result in increasing Hg exposure to top trophic level species. Atmospheric transport was thought to be the most important inputs of Hg in the Arctic along the spring time mercury depletion events (MDE's). However, it has recently been demonstrated that more than half of the Hg deposited during the MDE's was photoreduced rapidly and reemitted back into
2 the atmosphere (17). Outridge et al. (2008) suggested that the rate of biological uptake and trophic transfer from the large abiotic MMHg reservoir may be a key regulator through processes such as food-web ecology, ocean biogeochemistry and animal physiology and ecology (18).
This thesis includes an introduction, two manuscript style chapters and a conclusion. The major premise of this thesis was to investigate the linkage between Hg and carbon in zooplankton with oceanographic processes in two areas of the Canadian High Arctic: the
North Water Polynya in northern Baffin Bay and the Mackenzie Shelf-Beaufort Sea in the western part of the Arctic.
The second chapter of this thesis deals with the relationships between Hg and stable isotopes of carbon (813C) in marine zooplankton with water masses in the North Water
Polynya and to assess and explain the spatial and inter-species (between genus) variability of total mercury (THg) and methyl mercury (MMHg) among three keystone zooplankton genus; Calanus spp., Themisto spp. and Euchaeta spp. Measurements of stable-isotopes of carbon (813C) and nitrogen (815N) were used to help understand food web structure and determine Hg sources. Depending on the ecology of the species, zooplankton organisms were highly related to the surrounding water masses and on their physical environment as
Hg concentrations in lower trophic level species seemed to be strongly coupled to the chemistry at specific water column depths.
3 The third chapter of this thesis concerns the Canadian Western Arctic along the south eastern part of Beaufort Sea, the Mackenzie Shelf and the Amundsen Gulf using the same approach outlined above for the NOW.
In both areas of this study, the findings suggest that differing water masses are, at least in part, responsible for the assimilation of Hg and carbon in lower trophic level species. In the
North Water polynya, high THg concentrations in water appear to reflect the correspondingly high concentrations of THg and MMHg measured in Calanus spp. and
Euchaeta spp. Sub-glacial melt from the Prince of Wales ice cap (POW) was found to be a potential major source of mercury to the Smith Sound region of the North Water polynya.
On the Mackenzie shelf - Amundsen Gulf area, surface water was fresher in the western part of the Mackenzie Shelf and was strongly linked to the Mackenzie River. The results suggest that the higher THg concentrations found in zooplankton were associated with the delivery of Hg via the Mackenzie River.
This study used a biophysical coupling approach and is the first attempt to link mercury in zooplankton with water masses properties and stable isotopes of carbon and nitrogen. This research illustrated that studies linking the biology of a zooplankton species with the regional oceanography is an important factor which must be taken into account when trying to predict mercury uptake at higher trophic levels and assist in monitoring the impacts of a changing environment such as the Arctic.
4 References
(1) McCarthy, J. J.; Canziani, O. F.; Leary, N. A.; and, D. D. J.; K.S.White Cambridge University Press 2001, 1032 pp. (2) McBean, G.; Genrikh, A.; Deliang, C; Forland, E.; Fyfe, J.; Pavel, Y.; Groisman, R.; Melling, H.; Vose, R.; Whitfield, H. Arctic Climate Impact Assessment 2005, 22-60. (3) ACIA Cambridge University Press 2004. (4) Barber, D.; Marsden, R.; Minnett, P.; Ingram, G.; Fortier, L. Atmosphere-Ocean 2001, 39, 163-166. (5) IPCC 2007: Climate Change 2007 - The Physical Science Basis, 2007, ISBN-13: 9780521705967. (6) Macdonald, R. W.; Harner, T.; Fyfe, J. Science of the Total Environment 2005, 332, 5-86. (7) Prinsenberg, S. J.; Hamilton, J. Atmosphere-ocean 2005, 43,1-22. (8) Deutch B., D. J., Pedersen H.S., Asmund G., Mteller P. and Hansen J.C. The Science of The Total Environment 2006, 370, 372-381. (9) Skarra, H.; Kaartvedt, S. Marine Ecology Progress Series 2003,249, 215-222. (10) Auel, H.; Werner, I. Journal of experimental marine biology and ecology 2003, 296,183-197. (11) Dalpado, P.; Borkner, N.; Bogstad, B.; Mehl, S. Journal of Marine Science 2001, 58, 876-895. (12) Morel, F. M. M.; Kraepiel, A.M.L.; Amyot, M. Annu. Rev. Ecol. Syst. 1998, 29, 543-566. (13) Lockhart, W. L.; Stern, G. A.; Wagemann, R.; Hunt, R. V.; Metner, D. A.; DeLaronde, J.; Dunn, B.; Stewart, R. E. A.; Hyatt, C. K.; Harwood, L.; Mount, K. Science of the Total Environment 2005, 351-352, 391-412. (14) Barkay, T.; Poulain, A. J. Federation of European Microbiological Societies 2007, 59, 232-241. (15) Leitch, D. R.; Carrie, J.; Lean, D.; Macdonald, R. W.; Stern, G. A.; Wang, F. Science of the Total Environment 2006, xx, xxx-xxx. (16) Loseto L.L.; Stern, G. A.; Deibel D.; Connelly, T.L.; Prokopowicz, A.; Lean, D.R.S.; Fortier, L.; Ferguson, S.H. Journal of Marine Systems 2007, (In Press). (17) Kirk, J. L.; Louis, V. L. S.; Sharp, M. J. Environmental Science and Technology 2006, 40, 7590. doi:7510.1021/ES061299. (18) Outridge, P.M.; Macdonald, R. W.; Wang, F.; Stern, G.A.; Dastoor, A.P. Environmental Chemistry 2008, 5, 89. doi:10.1071/EN08002
5 CHAPTER 2
Linkage between Mercury and Oceanographic Processes in Marine Pelagic Zooplankton in the North Water Polynya, August and September 2005-2006
By Corinne Pomerleau Abstract
The North Water (NOW) Polynya is an important feeding, mating and over wintering ground for marine mammals. The study was therefore designed to investigate relationships between mercury and stable isotope of carbon in marine pelagic zooplankton with water masses and the resulting implications for marine mammals exploiting this area. In order to help understand the linkages between mercury uptake and zooplankton diet, measurements of total mercury (THg), methylmercury (MMHg) and stable isotopes of carbon (813C) and nitrogen (515N) were performed on three key genus of zooplankton collected in the North
Water Polynya in late summers of 2005 and 2006. Water masses were differentiated by
1 Q measurements of temperature, salinity, 8 O and nutrients. On the western (Ellesmere
Island) side of the study area, water masses are comprised primarily of cold Arctic waters characterized by a deep surface mixed layer on top of a thick layer of near-freezing water of considerably higher salinity. The eastern (Greenland) side is largely dominated by the inflow of Atlantic water and had a shallower surface mixed layer and an intermediate layer of warmer water of slightly higher salinity. In general, the Arctic waters were found to be more depleted in 8180 and higher in THg relative to Atlantic water. A strong positive correlation (^=0.82, p<0.05) was observed between mean THg (surface to 100 m in depth) concentrations and latitude. The maximum THg value in sea water (2.24 ng/L) was observed at station 118 near the coast of Ellesmere Island. High THg concentrations in water at Station 118 also seem to reflect the correspondingly high concentrations of THg and MMHg measured in Calanus spp. (19.2 ±1.2 and 7.2 ng/g) and Euchaeta spp. (83.4 ±
23.7 and 50.0 ng/g). The results suggest that differing water masses may be responsible for
7 part of the assimilation of the mercury and carbon in lower trophic level species.
1 a Measurements of depleted 8 O, lower salinity and nitrate levels and high THg levels in the water column at Station 118 suggest that sub-glacial melt from the Prince of Wales ice cap
(POW) could be a source of mercury to the Smith Sound region of the NOW polynya.
Since zooplankton had higher levels of MMHg in the north-western part of Baffin Bay, marine mammals and fishes feeding in these areas could therefore be exposed to higher levels of mercury. Mercury cycling and uptake by higher trophic level animals may also vary depending on location and time of the year.
Introduction
The North Water Polynya (NOW) is one of the most productive marine areas at higher latitudes and is thus threatened by climate modification and variability (1). It is located in the northern part of Baffin Bay (~75°N and 78°N) between Ellesmere Island and West-
Greenland and is bounded to the North by Kane Basin. Southward winds and ocean advection of sea ice are primarily responsible for the formation and maintenance of this large (~80 000 km2) recurring polynya (2). In winter, an ice bridge forms across northern
Smith Sound and prevents ice from entering the coastal polynya (3).
Interactions along fronts of imported water masses originating from the North Atlantic via the West Greenland Current and from the Arctic Ocean via Smith and Jones Sound are responsible for the unique water-column characteristics of this region (4,5). West
8 Greenland and Baffin currents form a cyclonic circulation pattern as the West Greenland current, associated with relatively warm and salty water, crosses Baffin Bay at about 75°N to join waters from the Canadian Arctic Archipelago (4). Southward movement of Arctic water (cold fresh surface layer) dominates in the NOW Polynya with the strongest flow
occurring in Smith Sound east of Devon Island (4,6).
Over the last three decades, an increase in the inflow of relatively warm and saline Atlantic water masses into the Arctic Ocean has been observed (7,8). According to Hays et al. (9),
marine pelagic ecosystems, and particularly zooplankton, are expected to be strongly
affected by hydrographic changes and variations in water mass distribution and advection.
Due to the ice dynamics, the physical properties of the water column produced by the
regional circulation pattern and the earlier light absorption in spring, primary productivity
is higher in the NOW Polynya than any other region located above the Arctic Circle (10).
The availability of food and the reduced ice cover in the winter makes this region
accessible year round for a wide range of marine mammal and bird species (11).
Although Hg is naturally present in the Arctic, anthropogenic inputs occur via long range
atmospheric transport of predominantly elemental gaseous mercury (GEM; Hg ), ocean and
sea ice transport, riverine inputs and coastal erosion (12). In addition, recent results
suggest that climate change will have a major impact on the process and pathways which
determine how Hg cycles through the aquatic marine Arctic ecosystem (12). Hg in the form
of mono-methylmercury (MMHg) is a known neurotoxin causing reproductive,
immunosuppressive, and neurobehavioral risks in biota and Minamata disease in humans
9 (13). Produced mainly by microbial methylation of inorganic mercury, Hg (II), in the aquatic environment, MMHg bioaccumulates in organisms over time, and biomagnifies at each trophic level (14). As a result, Hg concentrations at ultra-trace levels in water can reach toxic levels in top predators.
The discovery of the tropospheric mercury depletion events (MDEs) in the Arctic coastal environment in the mid-1990s (15) provided a potential mechanism of increased atmospheric Hg deposition in Arctic coastal regions after polar sunrise. However, further studies suggest that much of the Hg deposited in snow during MDEs is photo-reduced and re-emitted back to the atmosphere, and may not impinge significantly on the Arctic marine ecosystem (16,17). Furthermore, median atmospheric Hg concentrations in the Arctic have remained essentially constant for at least the past 10 years (16,18). Along with the MDEs finding, St. Louis et al. (19) recently proposed that open water areas, for instance polynyas and ice leads, were net sources of GEM and dimethyl mercury (DMHg) to the surrounding atmosphere. Atmospheric DMHg could then undergo transformation to MMHg and deposit directly into nearby snowpacks which would maintain significant loads of Hg (II). Other processes such as riverine Hg discharge, direct terrestrial Hg input from melted permafrost and coastal erosion (20), oceanic Hg transport, sea ice loss, marine mammal habitats, feeding patterns and food web structures (21) are thought to play an important role.
Moreover, processes at the base of the food web, including match-mismatch between large phytoplankton bloom and zooplankton grazers biomass and possible impacts of climate change at the ocean biogeochemistry level could impact both the phytoplankton and zooplankton and therefore change biotic Hg route (12).
10 There is a variety of significant human and ecological health issues associated with
elevated levels of both inorganic and organic Hg compounds in the Arctic marine food web, since many of its components are an important part of the Inuit traditional diet (22).
Energy flow in marine food web from primary carbon fixation through higher trophic level
consumers passes through a key complex component composed of various herbivorous and
carnivorous zooplankton (23). The role of zooplankton in contaminant transfer and energy
flux in the NOW pelagic food web is crucial since they feed at the base of the marine food
web and are themselves a direct food source for many species of fish, birds and marine
mammals (24-26). The use of stable isotopes of nitrogen and carbon has been largely
discussed in many previous studies as a powerful tool in determining food web structure,
energy pathways and contaminant behaviour and transfer (27-30). Stable isotope ratio of
nitrogen (15N/14N) have been used to assess trophic position as 15N is enriched compared to
14N with increasing trophic level (3.8%o of increase with each trophic level) (31). On the
other hand, stable isotope ratio of carbon ( C/ C) has a lower fractionation (0.8 to l%o)
and allows distinguishing source of primary production in a given food web (32).
When studying a marine system such as the NOW polynya, there is a need to include
several types of abiotic parameters in order to describe and better understand this unique
ecosystem. To identify water masses, salinity, water temperature, 5180 and nutrients
(nitrate, nitrite, phosphate, N:P ratio) are key factors that allow to distinguish between
Arctic, Pacific and Atlantic waters.
11 The aim of this paper was to assess and explain the spatial and inter-specie variability of
Hg in three keystone zooplankton genus across the North Water Polynya. To do this we attempted to determine how the biology of the different zooplankton genus, Calanus spp.,
Themisto spp. and Euchaeta spp. along with water masses properties are linked together with Hg uptake and stable isotopes of carbon. Depending on the specific biology of the species (diel vertical migration patterns, feeding behaviour), the exposure of zooplankton to
Hg was found to be strongly coupled to the seawater chemistry at specific water column depths.
Materials and Methods
Sampling was performed onboard the research Icebreaker CCGS Amundsen during the
2005 (05/08/05 to 15/09/05) and 2006 (18/08/06 to 27/09/06) late summer cruises in the
Canadian High Arctic. Figure 1 shows the sampling locations across the North Water
Polynya.
Water collection and analysis
Water samples were collected with 24 12-L Niskin bottles attached to a rosette sampler equipped with Seabird 911+ CTD (Sea-Bird Electronics, Inc.) for salinity, 8180 isotope,
THg and nutrients. Salinity and 8180 water samples were collected in 125 ml and 25 ml
12 Figure 1. Sampling locations in the North Water Polynya (NOW). Red circles represent stations where zooplankton was collected, red circles with a green border represent Hg water collection stations and the black dots represent the CTD stations.
«2**f
WW 851* 80°W TS°W WW t&°W Miff
13 glass bottles, respectively, and were kept refrigerated pending analysis. Salinity samples were analysed onboard the ship with an autosal Guildline Instruments model 8400B (range
0.005 to 42 psu). 6180 samples were analysed at the G.G. Hatch Isotope Laboratory at
University of Ottawa using the Gasbench + Deltaplus XP isotope ratio mass spectrometer
(Thermo Finnigan, Germany).
THg samples were collected in new sterilized Falcon polypropylene tubes (VWR), spiked with 0.5% Optima grade HC1 (Fisher Scientific) and were double bagged in polyethylene
Ziploc bags and transported in coolers to the laboratory where they were refrigerated until analysis. THg analysis was conducted using cold-vapour atomic fluorescence spectroscopy
(CVAFS) on a Tekran 2600 Hg analyser at UCTEL (University of Manitoba Ultra Clean
Trace Elements Laboratory), following the U.S. EPA Method 1631 (U.S. EPA, 2002) with a method detection limit of 0.2 ng/L. Certified reference materials ORMS-2 and ORMS-3
(NRCC) were used for quality control.
Nutrient samples were filtered online through 5.0 urn polycarbonate filters (Poretics
Corporation) and collected into acid-cleaned (10% HC1) polypropylene tubes after four rinses. Samples were stored at 4°C in the dark. The concentrations of nitrate (NO3"), nitrite
(NO2") and phosphate (PO43) were measured within one hour of collection, using automated colorimetric methods adapted from Grasshoff (1999) on a Bran+Luebbe Auto-
Analyzer 3 (33).
14 Zooplankton collection and analysis
Zooplankton samples were collected at 4 stations in 2005 and 8 stations in 2006 with a vertically towed Monster net, a set of 4 adjacent 1-m2 frame nets (mesh size 200 urn & 500 urn), from near the bottom to the surface and by trawling an oblique rectangular mid-water trawl (mesh size 1600 urn) or an oblique Tucker net (mesh size 2x500 urn) in the surface layer from 100 m depth to the surface. Samples were placed into 30 ml plastic vials and/or whirl-pak bags and were kept frozen at -20°C until further analysis for THg and MMHg.
Representative sub-samples of individual zooplankton genera were placed in 4 ml glass vials for stable isotope analysis (SIA). Three keystone zooplankton genus were included in this study: the herbivorous copepod Calanus spp. (mostly adult Calanus hyperboreus), the hyperiid amphipod Themisto spp. (mostly adult Themisto libelluld) and carnivorous copepod Euchaeta spp.
THg analysis was conducted at the Freshwater Institute, Department of Fisheries and
Oceans Canada in Winnipeg, Manitoba with cold vapour atomic absorption spectroscopy
(CVAAS) on a 3200 Elemental Mercury Detector with a detection limit of 0.001 \ig/g (dry weight). Prior to Hg analysis, zooplankton samples were freeze dried and a small amount
(~0.15g dw) of whole body composite of zooplankton samples, references materials (2976
Mussel Tissue, TORT-1 and DOLT-3) and calibration standards were acid digested with a hydrochloridric-nitric acid mixture 3:1 (HC1; HN03) and heated at 90°C for 4 hours, cooled down and brought to a final volume of 25 ml with distilled water.
15 MMHg analysis was conducted at the University of Ottawa by Gas Chromatography
Atomic Fluorescence Spectroscopy (GCAFS) with ECD detector following methods from
Uthe et. al. (1972) and Cai (1997) (34-35). A 0.2 g freeze dried sample was placed in a 20 ml scintillation vial with a Teflon lid then a 5 ml aliquot of 6M KOH was added to each vial and the samples were placed on an orbital shaker for 4 hours. Samples were acidified using a 6M HC1, then a 5 ml aliquot of a 3:1 KBr:Cu2S04 was added, followed by the addition of 5 ml of dichloromethane (DCM) then placed on the orbital shaker overnight.
Samples were centrifuged and 2 ml DCM was removed and placed in a 7 ml glass vial. One ml of sodium thiosulfate solution was added to the samples and placed on the orbital shaker for 45 minutes. Samples were centrifuged, and a 0.5 ml aliquot of the aqueous layer was removed and placed into a micro-centrifuge tube. Three hundreds ul of 3:1 KBr:Cu2S04 and 200 ul DCM was added to each micro-centrifuge tube. Samples were placed on the orbital shaker for 15 minutes, and centrifuged for 2 minutes. A 150 ul sub-sample of DCM was extracted and placed in GC vials with glass inserts.
Carbon and nitrogen isotopic analyses were performed at the University of Winnipeg
Isotope Laboratory (UWIL) by continuous flow ion ratio mass spectrometry (CF-IRMS) on a GV-Instruments® IsoPrime attached to a peripheral temperature controlled
Euro Vector® elemental analyzer. Sub-samples of whole-body composites of invertebrates were baked in an oven at 60°C for several days (to remove excess moisture) and the dried samples (1-2 mg) of different taxa were sent to the UWIL for 13C/12C and 15N/14N isotope ratio analyses. Replicate measurements were done for every 10 samples and triplicate measurements for every 15 samples. The CO2 and N2 gases produced were used to obtain
16 8 values for carbon and nitrogen ratios, which deviated per million (%o) from the standards used.
5 R%0 = ((Rsample/Rsta„dard)-l]*1000
where R is the 13C/12C or 15N/14N ratio in the sample and the standard, respectively.
Internally calibrated C/N standards were used intermittently with samples for accuracy and calibration throughout the entire analysis. Since lipid extraction may alter the interpretation of food web structure by shifting the entire food web positively in both 813C and 515N directions, no lipid extraction of the samples were made in this study (36).
Statistical Analysis
Statistical tests were performed using SYSTAT Software version 11.0. The significance level used for all tests was p<0.05. A General Linear Model (GLM estimate model) using
THg as the dependent variable coupled with station, year and station*year as the independent variables was used to assess the effect of station and/or year on THg. Since no significant effect was found, the 2005 and 2006 data were pooled together. Principal component analysis (PCA) was use to identify a smaller set of uncorrelated set of factors
(orthogonal or independent) among the abiotic parameters and THg levels measured in the
NOW at several depths. Least squares linear regression was used to determine correlation between THg, MMHg, %MMHg and 813C with all the abiotic parameters including position (latitude and longitude), temperature, 8180, salinity, percent Pacific water and nutrients (nitrate, nitrite, phosphate and N:P ratio). Visual graphical residual analysis was
17 performed at each step. Analysis of Variance (ANOVA) was used to assess for differences between sampling locations and stable isotope values.
Results and Discussion
Water masses structure in the North Water Polynya and linkage with mercury concentrations in sea water.
Figure 2 shows the two way water transfer in Smith Sound at the southern edge of Nares
Strait (4). Below a deep polar mixed layer, a narrow wall-bounded flow on the western side consists primarily of the much colder and more saline Arctic source waters and extends to over five kilometres from the coastline between 100 and 200 meters. The eastern side had a shallower surface mixed layer and an intermediate layer of warmer water of slightly higher salinity. As such, the area of study was divided into 4 distinct transects; three longitudinal and one latitudinal (Figure 3). Figures 4 (a-e) to 7 (a-e) show the temperature, salinity, nitrate + nitrite, phosphate and the N:P ratio contour plots for the sampling transects.
Transect A consisted of stations 127, 129, 130 and 131, Transect B consisted of stations
118, 119, 120, 121, 122, 123, 124, 125 and 126, and Transect C consisted of stations 101,
102, 103, 104, 105, 106, 108, 109, 111, 112, 113, 114 and 115. Latitudinal Transect D
(132, 127, 118 and 101) follows the Arctic water mass along the eastern coastline of
Ellesmere Island. Water THg concentrations, where available along the sampling transects, are superimposed onto each of the 5 contour maps. Table 1 summarizes the values for salinity, 5180, temperature, THg levels, nitrate, phosphate and chlorophyll a maximum at surface, 25, 50, 100 and 200 m at each station.
18 Figure 2. Schematic cross-section of ocean circulation beneath the NOW region. Circled crosses and dots indicate current directed into and out of the plane of the figure, respectively. Small arrows represent the circulation in the vertical plane (4).
-40 -20 0 2© 40 Distance (km)
19 Figure 3. NOW Polynya transects. A: 127 to 131, B: 118 to 126, C: 101 to 115 and D: 132-127-118-101.
M'H
ao'N
7fN
7n»
WW WW WW 7SW WW IW
20 Table 1. Summary table of salinity, 8180, temperature, THg levels , nitrate, phosphate and chlorophyll a maximum at surface, 25, 50, 100 and 200 m at each of the 8 stations (mean ± SE).
18 Station Latitude (dd) Longitude (dd) Depth (m) Salinity (psu) B 0 O) T(X) THg (ng/L) NOj(uM) P04(uM) Chl.a Max. (ug/L) 132 79.00050 72.2772 Surface 30.1762 ± 0.0003 -3.00 ± 0.10 -0.51 0.00 0.47 0.62 (19m) 25 32.1542 ±0.0003 -2.34 ± 0.10 -1.31 3.23 0.79 50 32.7231 ± 0.0001 -1.76 ±0.10 -1.44 7.28 0.98 100 33.4080 ± 0.0003 -1.16 10.62 1.07 200 33.9560 ± 0.0003 -0.60 ±0.10 -0.56 13.17 1.11 127 78.29600 74.3320 Surface 30.6974 ± 0.0001 -2.98 ±0.10 -1.50 1.733 ±0.169 0.71 0.56 2.66 (10m) 25 31.1949 ±0.0004 -2.91±0.10 -1.40 2.56 0.77 50 31.9101 ±0.0014 -2.51 ±0.10 -1.42 4.89 0.95 100 32.7696 ± 0.0008 -1.27 0.764 ± 0.331 7.91 0.97 200 33.9090 ± 0.0001 -0.67 ±0.10 -0.63 0.849 ±0.139 12.38 1.10 118 77.3732 76.6970 Surface 31.0392 ±0.0003 -2.09 ±0.10 -1.29 1.164 ±0.203 0.34 0.49 2.50 (23m) 25 31.1049 ±0.0004 -2.28 ±0.10 -1.32 0.64 0.53 50 31.3453 ±0.0001 -2.50 ± 0.07 -1.21 1.23 0.60 100 32.1225 ±0.0001 -0.26 2.239 3.94 0.79 200 33.2894 ± 0.0002 -1.24 ±0.07 -1.16 1.371 ±0.136 8.28 1.02 101 76.4062 77.2910 Surface 31.4409 ±0.0007 -2.32 ± 0.07 -0.12 0.698 ±0.013 0.11 0.46 1.93 (25m) 25 31.9140 ±0.0005 -2.09 ± 0.07 0.24 0.719 ±0.030 2.31 0.73 50 32.5815 ±0.0003 -1.89 ±0.07 -0.42 0.567 ± 0.013 4.17 0.88 100 33.0865 ± 0.0003 -1.15 0.353 ±0.150 7.90 1.05 200 33.6437 ±0.0013 -0.96 ± 0.07 -1.00 0.555 ± 0.024 10.92 1.01 108 76.25167 74.5970 Surface 32.1719 ± 0.0006 -1.76 ±0.07 0.80 0.610 ±0.047 0.49 0.36 2.93 (6m) 25 32.3498 ± 0.0007 -1.67 ±0.07 0.64 0.562 ± 0.068 2.17 0.51 50 32.6553 ±0.0010 -1.57 ±0.07 0.49 0.759 ±0.019 5.28 0.8 100 33.3837 ± 0.0003 -1.06 0.598 ± 0.038 9.39 1.02 200 33.8203 ±0.0015 0.00 ± 0.07 -0.80 0.739 ± 0.014 12.40 1.06 115 76.3495 71.2082 Surface 32.5699 ± 0.0004 -1.13 ±0.07 2.32 0.846 ± 0.061 0.01 0.26 5.25 (20m) 25 33.4352 10.0003 -0.86 ± 0.07 -0.96 0.656 ± 0.008 3.63 0.47 50 33.5456 ± 0.0014 -0.77 ± 0.07 -1.16 0.686 ±0.145 9.50 0.86 100 33.6981 ± 0.0000 -0.38 0.707 ± 0.051 12.46 1.02 200 34.1052 ±0.0007 -0.34 ± 0.07 1.41 0.630 ± 0.012 16.49 1.22 126 77.3497 73.4447 Surface 32.1951 ±0.0003 -1.37 ±0.10 2.57 0.13 0.22 1.22 (22m) 25 32.8507 ±0.0001 -0.95 ±0.10 1.38 2.84 0.57 50 33.3615 ±0.0002 -0.40 ±0.10 -0.37 7.95 0.9 100 33.6624 ±0.0005 -0.94 10.86 1.01 200 34.0192 ±0.0003 0.15 ±0.10 0.40 14.53 1.21 131 78.3257 73.1862 Surface 32.1196 ±0.0003 -1.81 ±0.10 0.51 1.14 0.49 1.15 (7m) 25 32.6600 ±0.0004 -1.50 ±0.10 0.24 3.90 0.73 50 33.0351 ±0.0004 -1.41 ±0.10 -0.56 7.74 0.93 100 33.4449 ± 0.0007 -0.98 8.41 0.97 200 33.8681 ±0.0008 -0.63 ±0.14 -0.57 12.83 1.07
21 A) Northern Longitudinal Transect 127- 131
This is the most northerly of the longitudinal transect (-78.5 °N) and consists of 4 stations including one sampled for Hg (Station 127). The western side of this transect at station 127 is composed of a cold and fresher surface (0-50 m) and intermediate (50-100 m) layer due mainly to the predominance of Arctic waters moving down along the Ellesmere Island coastline and the Prince of Wales glacier (Fig. 4 a-b). The warm surface mixed layer (T >
0°) observed between stations 129 to 131 may be attributed to seasonal heating. The upper
150 m between 129 and 131 is characterized by a mixture of approximately 50% Atlantic and 50% Pacific water, values generally observed south of Kane Basin in Smith Sound
(37). Nutrient concentrations were similar along the entire transect. Low surface concentrations were correlated with lower salinities and higher concentrations in the deeper more saline waters (Fig. 4 c-e). This pattern is typical of Baffin Bay nutrient profiles and is due primarily to seasonal nutrient depletion and carbon export. A pool of warmer, phosphate depleted surface water (-0-30 m) was observed between 74.25 and 73.5°W.
Since the temperature of the Arctic outflow is below the value of-0.5°C, this warmer water layer must have originated in the West Greenland Current (4).
B) Middle Longitudinal Transect 118-126
This middle transect (-77.5 °N) consisted of nine stations including Station 118 that was sampled for Hg. Two main water masses were observed along this sampling line. The West
Greenland current was characterised by a warm water layer sandwiched between the 50 and
22 Figure 4. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio contour plots for the sampling transect 1 of the North Water Polynya. Water THg concentrations are superimposed onto each of the 5 contour maps for station 127. a) Temperature (°C) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
mmmHH
2091
Q. Q *00\
J004
n.s'w 74-w nrw 73°W Longitude
Hyperiid Amphipod: <*---• 25 m
b) Salinity (psu) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
T4.ITW WW n.s°w jrw Longitude Hyperiid Amphipod: ""_" 25-50 m
Calanoid Copepod: 150-200 m
23 c) Nitrate + Nitrite (MM) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
74.5°W 74°W 7i.5°W
Longitude
d) Phosphate (|JVI) Hg(ngfl_) 0.00 0.50 1.00 1.50 2.00 2.50
E
Q. 300H lea Q 400-1
05 600H IF
W.S1T WW T3.$°W 73°W Longitude
Calanoid Copepod: [ j 150-200 m
24 e) Ratio N:P Hg(ng/L) 0.00 0.50 100 1.50 ZOO 2.50
lis
74.5-W 73°W
Calanoid Copepod: « • 50 m
25 150 m marks which then expands westward (Fig. 5 a-b). The coldest water occurred west from station 121 and was defined by a strong salinity gradient with the freshet water on the surface. Corresponding increases in nitrogen, phosphate and the N:P ratios with depth were also observed in this region. Smith Sound waters were described as being low in nitrate, especially in the upper water column (Fig. 5c) (37). The eastern part of this transect had sub-surface waters more concentrated in nitrogen than the western side and, once again, this can be attributed to the West Greenland Current. Higher nitrogen concentrations in the
NOW polynya originate primarily from Atlantic waters (37) and this was observed between stations 126 at 100 m to 119 at 250 m. Depleted nutrient values were observed in the surface layer (0-100 m) from stations 118 to 121 and is likely associated with active biological uptake and activity that takes place throughout the summer. The structure of the surface layer is also influenced by processes including seasonal heating, sea ice melt and formation, glacial melt (icebergs and runoff), non-glacial runoff, net precipitation and mixing processes (37).
C) Southern Longitudinal Transect 101-115
This transect is consisted of stations 101 to 115 and is the most southerly of the three longitudinal sampling lines. Temperature and salinity plots indicated that the western side of Baffin Bay was characterised by a fresher surface layer overlaying a cold mixed layer between 50 and 250 m (Fig. 6 a-b). This is likely associated with the predominance of
Arctic waters coming through Smith Sound and Jones Sound near Devon Island. This
26 Figure 5. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio contour plots for the sampling transect 2 of the North Water Polynya. Water THg concentrations are superimposed onto each of the 5 contour maps for station 118. a) Temperature (°C) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
77*W WW WW WW Longitude Hyperiid Amphipod: •—»• 25 m
b) Salinity (psu) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
T7°W trw ww WW Longitude
Hyperiid Amphipod: r ""3 25-50 m
+ ""i Calanoid Copepod: L ! 150-200 m
27 c) Ntrate+Ntrite(|JV$ H3(rgq aoo aso too tso 201 250
77°W n°w WW WW Longitude
d) Phosphate (uM) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50
rrw 74°W Longitude
Calanoid Copepod: I j 150-200 m
28 e) Ratio N:P Hg(ngfl-) 0.00 0.50 1.00 1.50 2.00 2.50
rrw TS°W 7S°W 74"W Longitude
Calanoid Copepod: -* •• 50 m
29 fresher surface layer was also low in nitrogen and phosphorous levels, (Fig. 6 c-d).
Phosphorus concentrations in ocean surface waters are usually low (<1 um) primarily because of uptake by algae and bacteria (38), however, the lower N:P ratio (<8) measured between surface and 150 m at stations 101 to 108 (Fig. 6e) suggests that nitrogen is the limiting factor. On the Greenland side, a warmer and saltier intermediate layer was observed between 150 and 300 m which is attributed to a northward intrusion of Atlantic water through the West Greenland Current (T> 0 C). Interestingly, over 35 years ago it was reported that there was no flow of warm water to this latitude (39). Over the last few decades, however, an increase in the inflow of Atlantic water to the north has been observed (8). The south-eastern side of Baffin Bay is also enriched in nutrients with the highest concentrations occurring in water deeper than 200 m. This region is characterized by deep mixing and low stratification (40). The high nutrient values and N:P ratio in the deeper water of Station 115 is indicative of an effective biological pump and recycling of nutrients into the deeper waters.
D) Latitudinal Transect 132- 101
This is a north-south transect which follows along the eastern coastline of Ellesmere Island.
The sill in Kane Basin separates waters under 220 m in the north from those in Smith
Sound and waters below the sill have temperatures and salinities characteristic of northern
Baffin Bay (37). Station 132, the most northerly station, was largely influenced by cold arctic waters in the top 100 meters with temperatures reaching -1°C. Further south at station 127 even colder surface water temperatures were measured (< -1.25°C). A strong
30 Figure 6. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio contour plots for the sampling transect 1 of the North Water Polynya. Water THg concentrations are superimposed onto each of the 5 contour maps for station 101, 108 and 115. a) Temperature (°C) Hg(ng/L) Hg(ngfl-) Hg(ng/L) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20
WW mr n% rrw Longitude Hyperiid Amphipod: *-.-* 25 m
Salinity (psu) b) Hg.. (ng/L. ). Hg (ng/L) Hg (ng/L) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20
tee H
200 33.5
5 309^
tOAH nt 7*1* T2°W Longitude
Hyperiid Amphipod: f~ZZZ3 25-50 m
*•••••*» i Calanoid Copepod: [ j 150-200 m
31 c) Nitrate + Nitrite (uM) Hg(n^L) Hg(ngfl-) Hg(ng/L) 0.00 0.20 0/40 0.60 0.80 1,00 1,20 0.00 020 0.40 0.60 0.80 1.00 1.20 0.00 020 0.40 060 0.80 1.00 120
TTW WW 741* 7TW Longitude
d) Phosphate (uM) Hg(ng/L) Hg(ng/L) Hg(ng/L) 0.00 0.20 0.40 0.60 0.80 1,00 120 0.00 0.20 0:40 0.60'080 1.00 1.20 0.00 020 0.40 0.60 0.80 1.00 1.20
n°w mr ww WW Longitude
Calanoid Copepod: j 150-200 m
32 e) Ratio N:P
Hg(ng/L) Hg(ng/L) Hg(ng/L) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 00° "-20 ».40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 120
78^ 76-W 74°W TTW Longitude
Calanoid Copepod: * *• 50 m
33 Figure 7. a) temperature, b) salinity, c) nitrate + nitrite, d) phosphate and e) N:P ratio contour plots for the sampling transect 4 of the North Water Polynya. Water THg concentrations are superimposed onto each of the 5 contour maps for stations 127, 118 and 101. a) Temperature (°C) Hg(ngfl-) Hg(rtfL) Hg(ng/L) 0.00 0.50 1.00 ISO 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50
-0.75
mi nm rm Latitude
Hyperiid Amphipod: +—*• 25 m
Salinity (psu) b) Hg(ng/L) Hg(ng/L) Hg(ng/L) 0.00 0.50 1.00 1.50 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50
Hyperiid Amphipod: [•""_" 25-50 m
Calanoid Copepod: 150-200 m
34 c) Ntrate+Nitrite (jlty H3(ncfl.) hbQngq Hg(ngi.) OLOO OLSD 1.00 1.50 200 250 0.00 0.50 1.00 1.50 ZOO 250 0.00 0.50 1.00 1.50 200 250
Phosphate (MM) d) Hg(ng/L) Hg(ng/L) Hg(ngfl.) 0.00 0.50 1.00 1.50 200 2.50 0.00 0.50 1.00 1.50 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50
7TW WW rm Latitude
Calanoid Copepod: I j 150-200 m
35 e) Ratio N:P Hg(ng/L) Hg(ngrt_) Hg(ngfL) 0.00 0.50 1.00 1.50 ZOO 2.50 0.00 0.50 1.00 1.50 2.00 250 0.00 0.50 1.00 1.50 2.00 2.50
7TM Latitude
Calanoid Copepod: « *• 50 m
36 increasing salinity gradient was observed with depth along the entire transect. The lowest surface salinity, nitrogen and phosphate concentrations were measured at station 118. As discussed earlier, this may be associated with the sub-glacial melt from the Prince of Wales glacier. As was first reported by Falkner et al. (2006), a nutrient rich sub-surface southward flowing jet was observed along this entire transect (37). According to these authors, this nutrient rich water derived largely from the Bering Sea in the winter season. As noted by
Tremblay et al. (2002), nutrients must be supplied from the north in order to sustain high productivity in the NOW (41).
Total mercury water concentrations and profiles
THg water concentrations range from 0.35 to 2.24 ng/L at stations 101 and 118, respectively. Both samples were collected at a water column depth of 100 meters (Table 1,
Figures 4-7). Because of the limited THg water data, it is difficult to determine any strong relationship with the water mass characteristics discussed in the previous section. However,
THg levels were the lowest along the southern Transect C and the highest along Transect
D, in particular, station 118 and 127. High surface THg concentrations seem to be associated with colder water temperatures. PCA (see Methods section) was conducted to
examine pattern similarities and differences between temperature, THg, salinity, phosphate
and nitrate + nitrite concentrations with station number and depth. The resulting score and
loading plots are shown in Figure 8. The first and second principal components (or factors)
accounted for 56 and 27%, respectively, of the total variability in the data set. Not unexpectedly, phosphorous, nitrogen and salinity were strongly positively correlated to the
37 Figure 8. Principal Component Analysis (PCA) results, a) Factor Loading Plot and b) Score Plot for data measured in the North Water Polynya, 2005 and 2006.
Factor Loadings Plot Scores Plot
I.U i i i 3.01
TUGS
0.5 \ \ ^^^°F lOBJOOm 115 50m • _»1O»_20Om rS'-™1" 115 501 2 0-0 CM i^oum fajQi^ *'g27_5ooni » < 7^ ' ' ' 115 25m^ 0fl o r^C O -2.o -i.o ""-#*" e, D. -0.5 / TEMP<* 1 1 1 -1.0 -0.5 0.0 0.5 1.0 PCA1 (58%) -3.01 PCA1 (a) (b)
38 Atlantic waters lying between 50 to 500 meters. Most interesting though is that THg concentrations along the most southern transect were positively correlated with warmer surface waters (surface to 50 meters). Conversely, in the surface water at station 127, a negative correlation was observed between temperature and THg levels. The highest water
THg concentration was observed at station 118 in the slightly warmer water at 100 meters.
The higher THg levels in the colder water may be attributed to ice melt from the Prince of
Wales glacier and will be discussed further in the following section.
Prince of Wales subglacial runoff as a source of mercury to the North Water Polynya
Water masses on the western side of the NOW, along the Ellesmere Island, were comprised primarily of cold Arctic waters while the Greenland side was largely dominated by saltier
Atlantic waters (4). Atlantic waters are generally nitrate enriched relative to phosphate while Pacific waters tend to be phosphate-rich (42,43). Figure 9 (b,e,f) shows the 5180,
chlorophyll-a (Chl-a) max and THg values from surface to 200 meters for stations located
in the Arctic and Atlantic dominated waters. In general, the Arctic waters were more
depleted in 8180 and higher in THg. Chi a max concentrations peaked at station 115 and
range from 6 to 25 meters depth. A strong positive correlation (^=0.82, p<0.05) was
observed between mean THg (surface to 100 meter) concentrations and latitude. The
maximum THg value in sea water (2.24 ng/L) was observed at station 118 near the coast of
Ellesmere Island (Figure 9 f and Table 1). This station was located just east of the Prince of
Wales Icefield which is known to have greatest rate of snow accumulation compared to any
1 R
other icefield in the Canadian Arctic (44). As noted in Figure 9 (a,b,d), salinity, 8 O and
nitrate+nitrite concentrations at station 118 were, with a few exceptions, lower than values
39 Figure 9. Spatial trends of abiotic variables measured at surface, 25, 50, 100 and 200 m. a) salinity, b) 8180, c) temperature, d), nitrate levels, e) chlorophyll a max values and chlorophyll max depths and f) THg levels in water from the North Water Polynya.
40 normally associated with a Pacific water signal suggesting that meltwater from the eastern flanks of the glacier is entering into the North Water polynya in this region. The more depleted values of 8180 and lower salinity in the surface water at stations 127 and 132 suggest that glacial ice melt entered these areas as well. While the samples were collected in August, low elevation areas facing Baffin Bay tend to have both earlier melt onset and later freeze-up dates (45). Connections between surface and subglacial drainage on Arctic glaciers occur by abrupt hyrologically-driven propagation fractures from the surface to the bed. However, the onset of continuous flow through may be delayed by processes such as refreezing of the water that initially penetrated the fracture and thus resealing the connection (46). Bulk subglacial meltwater is thought to be composed of both quick flow and delayed flow components (47,48). The former component represents meltwater in rapid transit through well defined conduits in the glacial system while the delayed flow pertains to the slow passage of water at the ice-bedrock interface near the base of the glacier.
In a study of meltwater solute acquisition within subglacial environments, Wynn et al. (48)
15 reported enriched 8 NNo3 values in sub-oxic, delayed flow, glacial meltwater and postulated that microbial denitrification is an active component of nutrient cycling in the subglacial environment. This result could explain the depleted nitrate levels measured at
Station 118. Recently, St. Louis et al. (19) proposed that open water regions such as polynyas and ice leads were net sources of gaseous elemental mercury (GEM) and dimethyl mercury (DMHg) to the surrounding atmosphere. Atmospheric DMHg could then undergo transformation to MMHg and deposit directly into nearby snowpacks. In addition, the authors hypothesized that snowpacks receiving marine aerosol deposition of CI" and
41 deposition of inorganic Hg (II), for example during spring time Mercury Depletion Events
(MDEs), would maintain significant loads of Hg (II). Median wet/dry loads THg of 0.52 ng/L and MMHg 0.071 ng/L were reported in snow packs sampled in their study area.
Interestingly, the highest aerial loadings (25 ug THg m"2 and 0.009 ug MMHg m"2) reported by St-Louis et al. (19) were measured in snow pack collected at Talbot Inlet, very close to site 118. THg concentrations ranged from 1.53 to 4.06 ng/L (mean = 2.63 ng/L) in subglacial runoff collected in July 2001 and 2002 from the John Evans Glacier which is just north of the Prince of Wales ice cap (19). The depleted 5lsO, the lower salinity and nitrate levels and higher THg water concentration suggest that sub-glacial melt from the
Prince of Wales ice cap may have been a source of Hg to the Smith Sound region (Station
118) of the NOW polynya. Higher THg water concentrations at Station 118 also seem to reflect the correspondingly high concentrations of THg and MMHg measured in Calanus spp. In fact, THg and MMHg in Calanus were strongly positively correlated with the THg levels in water (0-100 m) (Figure 10 (a, c)). Interestingly, similar relationships were observed in Euchaeta (Fig. 10 b, d) but not in Themisto. Unfortunately, nutrients and THg concentrations at station 118 (100 m) could not be substantiated using a three components
(Arctic, Greenland, and sub-glacial melt water end members) two tracers (phosphate and nitrate) mixing model. Increasing both the sampling frequency and resolution during a future cruise would help resolve this issue by better defining the end member concentrations (49).
42 Figure 10. Relationships between THg levels in water and a) THg in Calanus spp., b) THg in Euchaeta spp., c) MMHg in Calanus spp. and d) MMHg in Euchaeta spp. from the North Water Polynya. a) b)
0.14! 0.14
0.12 0.12 1^ = 0.99 „'' p<0.0001^' 0.10 .
0.08 : I**
0.06
2 0.04 r = 0.93 : +'"' p<0.01 0.02 -
0.00 0.25 0.75 1.25 1.75 2.25 2.75 0.25 0.75 1.25 1.75 2.25 2.75
d)
- 0.06 ^. 1^ = 0.77 ',,-•" " " 0.05- • p<0.05„^
0.04 • ^^ _ 0.03- m
- 0.02 - r2 = 0.95 p<0.005 " -—•— ' 0.01
1 1 1 —i— 1 0.00 1 1 1 1- I 25 0.75 1.25 1.75 2.25 2.75 0.25 0.75 1.25 1.75 2.25 2.75 THg ng/L THg ng/L
43 Mercury levels and stable isotopes in zooplankton
Table 2 summarizes THg and MMHg levels, %MMHg, 815N and 513C in Calanus,
Euchaeta and Themisto spp. at each of the 8 sampling stations. Calanus had the lowest
THg concentrations among the three species with a mean level of 12.6 ± 3.0 ng g"1.
Euchaeta and Themisto had mean concentrations of 75.6 ± 24.2 and 48.8 ± 12.3 ng g"1, respectively. Similarly, Calanus had the lowest MMHg levels with a mean concentration of
4.8 ± 1.2 ng g"1. Themisto and Euchaeta had mean concentrations of 23.0 ± 3.4 and 39.0 ±
11.0 ng g"1, respectively. The percentage of MMHg in THg ranged from 38.2 ± 4.9 % in
Calanus to 50.8 ± 17.7 % and 52.5 ± 9.5 % in Themisto and Euchaeta, respectively. In an earlier study Campbell et al. (50) reported a NOW C. hyperboreus THg concentration of
25.0 ± 17 ng g"1 and of 20.0 ± 9 ng g"1 in T libellula. They also reported a MMHg concentration in C. hyperboreus of 2 A ± 1.3 ng g"1 and of 28.3 ± 0.8 ng g"1 in T. libellula.
THg concentrations in zooplankton are generally related to their trophic level with predatory genus having higher proportion of MMHg. While MMHg levels in zooplankton are thought to increase with body size, Kainz et al. (51) demonstrated that their MMHg concentrations were linked to both habitat and spatial distribution in the water column. In this study, several significant linear relationships were observed between THg, MMHg and
%MMHg for each of the three genus. THg and MMHg were strongly positively correlated in both Calanus (1^=0.76, p<0.01) and Euchaeta (^=0.65, p<0.05). THg in Themisto was strongly negatively correlated with %MMHg (r^=0.88, p<0.01). No significant positive correlations were observed between higher THg or MMHg levels with 815N (trophic level) in each of the genus species. Similar results were also reported by Braune et al. (52)
Several studies on the prey selection patterns by different species of Euchaeta at high
44 Table 2. Total mercury (THg), methyl mercury (MMHg), percent methyl mercury in THg (%MMHg), 813C and 815N values for Calanus spp., Euchaeta spp. and Themisto spp. at the 8 sampling stations (mean ± SE) in the North Water Polynya.
Station id. Taxonomic Group - Genus THg(ng/gdw)±SE MMHg(ng/gdw)±SE %MMHg 613C (%o) ± SE 515N(%o)±SE
132 Copepod Calanoid - Calanus spp. 9.9 ±1.0 4.6 ±0.2 46.2 -30.00 ±0.13 8.23 ±0.14
127 Copepod Calanoid - Calanus spp. 15.2 ±8.0 5.8 ±0.2 38.0 -29.61 ± 1.15 7.41 ± 0.20 Copepod Calanoid - Euchaeta spp. 127.2 ±13.4 55.7 43.8 -28.27 ± 0.08 11.67 ±0.06 Hyperiidea Amphipod - Adult Themisto spp. 37.7 ±1.3 22.8 ±1.3 60.4 -23.25 ±0.08 8.27 ± 0.06 131 Copepod Calanoid - Calanus spp. 114±1.2 3.7 ±0.1 32.5 -34.03 ±0.74 7.72 ± 0.08 Copepod Calanoid - Euchaeta spp. 67.3 ±0.0 43.2 ±0.0 64.2 -23.23 ±0.13 12.22 ± 0.07 Hyperiidea Amphipod - Adult Themisto spp. 52.4 ±4.6 24.7 ±1.1 47.1 -22.42 ±0.82 9.11 ±0.20 126 Copepod Calanoid - Calanus spp. 11.2±2.0 3.4 ±0.1 30.6 -33.94 ±0.11 8.12 ±0.11 Copepod Calanoid - Euchaeta spp. 69.7 ± 19.4 27.6 ±0.0 39.6 -31.71 ±0.11 10.25±0.11 Hyperiidea Amphipod - Adult Themisto spp. 50.9 ±3.3 22.5 ±0.8 44.1 -17.66 ±0.04 10.06 ±0.07 118 Copepod Calanoid - Calanus spp. 19.2 ±1.2 7.2 37.7 -26.97 ± 0.08 7.33 ± 0.06 Copepod Calanoid - Euchaeta spp. 83.4 ± 23.7 50.0 60.0 -25.72 ±0.08 10.67 ±0.06 Hyperiidea Amphipod - Adult Themisto spp. 28.2 ±1.4 23.6 ±1.8 83.7 -25.84 ±0.39 8.67 ± 0.27 115 Copepod Calanoid - Calanus spp. 10.6 ±0.8 4.8 ±0.2 45.4 -32.62 ±0.11 9.7 ±0.11 Copepod Calanoid - Euchaeta spp. 61.2 ±9.3 28.3 ±0.8 46.3 -25.53 ±0.13 11.35 ±0.07 Hyperiidea Amphipod - Adult Themisto spp. 63.4 ± 7.5 16.3 ±2.1 25.8 -22.64 ±1.88 11.21 ±0.23 108 Copepod Calanoid - Calanus spp. 12.3 ±1.9 4.3 34.9 -28.54 ± 0.35 7.43 ± 0.09 Copepod Calanoid - Euchaeta spp. 61.8± 11.9 32.4 52.4 -24.89 ± 0.06 10.51 ±0.07 Hyperiidea Amphipod - Adult Themisto spp. 48.4 ±4.2 23.4 ±5.8 48.3 -19.52 ±1.25 11.74 ±0.16 101 Copepod Calanoid - Calanus spp. 11.1 ±1.2 4.4 ±0.3 40.0 -23.90 ±0.06 7.70 ±0.07 Copepod Calanoid - Euchaeta spp. 58.7 ±2.3 35.8 60.9 -23.70 ± 0.06 13.21 ±0.07 Hyperiidea Amphipod - Adult Themisto spp. 60.2 ±2.8 27.7 ±1.9 46.0 -21.41 ±0.16 9.55 ±0.45
45 latitudes showed that Calanus spp. was a major part of the Euchaeta diet (53). This could explain why Calanus and Euchaeta were positively correlated with THg and MMHg levels as one of the accumulation pathways of MMHg in zooplankton is through ingestion of food
(54). As for Themis to, variations in the net accumulation strategy could explain the absence of a positive correlation between THg and %MMHg in THg (55). The difference in lipids storage between hyperiid amphipod and copepods vary in terms of metabolism, adaptation and trophic characteristics of the consumer (56). Thus, accumulation of MMHg is highly dependent upon the unique habitat and biology of the species considered. As indicated by their 815N, both Euchaeta and Themisto occupied a higher trophic position relative to
Calanus with mean values of 11.41 ± 1.06, 9.80 ± 1.29 and 7.96 ± 0.80 %o, respectively
(Table 2). ANOVA results indicated that significant differences in 815N occurred between locations for Calanus (F=13.83, df=7, p=0.012) and Themisto (F=23.25, df=6, p=0.000) but not in Euchaeta. A significant linear relationship between longitude and 813C (r^O.68, p=0.01) in Calanus revealed that 513C values were more enriched on the Ellesmere Island side and more depleted along the Greenland coast in Calanus. This longitudinal trend was not observed in the two predatory genus.
Linkage between biological and physical processes
In order to determine the linkage between Hg uptake and zooplankton diet, measurements of stable isotopes of carbon were performed and the relationships between these two parameters and water masses properties at several depths were examined. Stable isotopes of carbon is a useful tracer of primary carbon sources with a 813C (13C:12C) increase of <1% per trophic transfer (57). Most particulate organic carbon (POC) is derived from
46 phytoplankton and is the main source of food for zooplankton (58). Factors including rapid phytoplankton growth and large celled diatoms may reduce fractionation and produce an enriched zone (59). POC values vary according to location, depth and season. Also, the amount of faecal pellets in the water column may alter the value of POC and consequently the value of 8 C in zooplankton (60). Here, because the contribution of faecal pellets to the
S13C value of POC throughout the area of study is unknown, the fractionation of the POC or the assimilation in the grazers is unknown.
As noted in previous sections, a strong vertical salinity gradient was observed in the water
column between the surface and 200 m. As such our discussion is restricted to this depth range. Nutrient ratios of N:P, Si:P and Si:N were used here to help differentiate between
Atlantic and Arctic water masses and to understand primary productivity. While
zooplankton (biomass and taxonomic) vertical profile data was not yet available for the
samples collected during the 2006 ArcticNet cruise, the linkages found between water
column features (Figure 2, Table 2) and zooplankton THg and MMHg concentrations,
%MMHg and 813C (Table 3) in three main species are described in this section. Here, 813C was used as a predictor to determine where zooplankton may be feeding throughout the water column.
Longhurst et al. (1984) described the late summer vertical distribution of various
zooplankton species in northern Baffin Bay relative to water column features such as
temperature, salinity and chlorophyll a (61). They found that diel migration was virtually
absent in late summer and that their vertical distributions were driven primarily by seasonal
47 or ontogenic migration patterns. They reported that all species existed in water temperatures and salinity ranging from -1.9 to 3.0 °C and 29.5 to 34.5 psu, respectively.
Water temperature was the physiological limiting factor while salinity mainly impacted the sinking rates of particles. In the Smith Sound and Kane Basin regions, the chlorophyll a maxima occurred in the surface mixed layer at 15-22 meters of depth. Highest relative abundances of adult and older stage (IV and V) Calanus species occurred within three depths ranges; surface (~5-30 meters), the base of the thermocline (-25-50 meters) and near the surface at the Atlantic water layer (~200 meters) (61). Daase et al. (2007) studied the relationships between salinity, temperature and copepod abundance for the Arctic species C. hyperboreus and found that they were more abundant in the colder and fresher
Arctic waters (62). Similarly, the numbers of C. glacialis decreased with temperature and
salinity at depths < 500 meters. Interestingly, sub-surface hydrography between 50-150 m was generally found to be a better predictor for Calanus spp. abundance than near-surface conditions, the former generally explaining up to 50% of the variability in abundance of each species.
Calanus spp.
Calanus hyperboreus investigated in this study were mainly the larger adult older staged
animals. Prokopowicz et al. (2002) reported that C. hyperboreus was the dominant taxa
among all Calanus species in the North Water Polynya (63). Because of their large biomass, copepods have key roles in energy flow and material recycling through the entire
water column (64). Open ocean currents have been shown to play an important role in the pelagic spatial distribution of zooplankton at high latitudes and copepods have been
48 considered as a good potential marker of climatic changes through water-mass indicator
(65). Yet, it remains unknown as to how zooplankton are going to be affected by water mass changes that are already being observed at higher latitudes (7,8,66). Table 3 shows the significant linear relationships observed between the Calanus THg and MMHg concentrations and 813C values with a range of water column features across all the sampling stations. For Calanus spp., THg, MMHg and S13C were correlated with water mass properties between 25-50 m and 150-200 m. As noted earlier in this section and in
Table 2, both THg and MMHg levels in zooplankton were higher at stations located along the Ellesmere Island coast (127 and 118) and were correlated with THg water concentrations. Calanus spp. has been observed to aggregate in the water column at about
~3-4 m above or within the chlorophyll-a maximum depth range. This observation was confirmed in North-eastern Baffin Bay in late July and beginning of August where the highest copepods abundance was observed just above the thermocline and halocline at depth usually varying between 20 and 30 meters (67). This could explain why both Hg and
8 C were correlated with salinity in surface waters. 8 C was also correlated with salinity between 150 and 200 m. Copepods generally start their descent in the late summer months in preparation for winter diapause into deeper sections of the water column (>500 m) (68).
A study by Sato et al. (2002) in the Barents Sea showed that lipid contents in Calanus spp. was the highest in September suggesting that the correlation observed between S13C and salinity near the Atlantic layer is likely linked to feeding patterns of calanoid copepods
(69). In this study a more depleted 813C signature was measured at higher salinity and phosphate concentrations between the 150-200 m (i.e. Fig. 6 (b, e), Fig. 7 (b, e) and Table
2). It is well known that ocean currents that carry water from the polar and temperate
49 regions increase the marine productivity in the shelf areas of Southwest Greenland (70).
Moreover, mechanisms of maintenance and formation of the NOW Polynya are known to produce upwelling of warm subsurface water along the west coast of Greenland (71). Of
the three species included in this study, C. hyperboreus had the most depleted mean 8 C
value ranging from - 34.0%o at station 131 to - 23.9%o at station 101. Variations between
stations were relatively pronounced as 513C spanned by about 10%o. A significant
longitudinal trend was observed with 813C values becoming more depleted moving west
toward Greenland. A less depleted value is generally indicative of more frequent upwelling
events (72).
Euchaeta spp.
Longurst et al. (1984) described Euchaeta has an interzonal diel migrant where both near
surface and deep concentrations occurred together (61). Kaartvedt et al. (73) also found
Euchaeta to have a bi-model vertical distribution with a predominant upper water mode in
summer time along with a more common deep water mode through fall and early winter.
They also noted that feeding occurs toward the surface especially for the smaller size while
the larger females were observed to be foraging successfully in deep water. Results from
Vestheim et al. (74) suggested that ovigerous females and individuals with great energy
reserves to a large extent prioritize predator avoidance in deep water versus feeding in the
upper part of the water column. Numerous factors including food availability, predator
avoidance, vertical water column stratification and light have been recognized to influence
diel vertical migration (DVM) (75). Euchaeta has been described as a cruising raptor
feeding on a variety of smaller zooplankton which include Calanus and cod larvae which
50 Table 3. Significant interactions between THg, MMHg, %MMHg of THg and 8 C in Calanus, Euchaeta and Themisto with salinity, 8180, temperature and percent Pacific water. Dep. Var. is the dependant variable, r2 is the correlation coefficient and p is the level of significance of the test.
Genus Dep.Var. Depth (m)* Salinity (psu) 5lsO (%o) Temperature (°C) % Pacific water ** P P P P THg 5 0.62 0.039 Calanus THg 25-50 0.75 0.005 THg 150-200 0.64 0.019 0.78 0.004 MMHg 5-25 0.59 0.026 MMHg 25-50 0.73 0.008 0.57 0.03 MMHg 150-200 0.54 0.044 0.57 0.043 %MMHg 25 0.52 0.045 513C 50-100 0.61 0.03 513C 150-200 0.52 0.05 THg 5 0.57 0.036 0.56 0.045 Euchaeta MMHg 5-10 0.83 0.004 MMHg 5-25 0.72 0.016 MMHg 5-50 0.75 0.012 0.77 0.01 513C 200 0.50 0.05 Themisto THg 25-50 0.71 0.018 THg 150-200 0.70 0.021 MMHg 25-100 0.67 0.028 MMHg 150-200 0.68 0.03 %MMHg 25-50 0.84 0.002 %MMHg 150-200 0.60 0.035 0.94 0.001 513C 25 0.81 0.006 513C 200 0.74 0.013 * Depths sampled - Salinity (surface, 2.5, 5, 7.5,10, 25, 50,100,150,200 m); 8180 (surface, 2.5, 5, 7.5,10, 25, 50, 200 m); Temperature (5,10,25,50,100,150, 200); %Pacific (5,10,25, 50, 100,125,150, 200 m). Mean parameter values were used when consecutive depths showed significant correlations. * *Calculated by Jean-Eric Tremblay based on the method used by Jones et al. (1998) (76).
51 would in turn explain its relatively mean value of enriched carbon signal found throughout the study area (54). As with Calanus, the carnivorous copepod Euchaeta spp. had a surface and a deeper water vertical distribution. The correlation found between 813C and 8180 at 200 m suggest that some Euchaeta spp. were probably feeding at that depth.
THg was correlated with salinity and 8180 and MMHg with all four parameters (salinity,
8 O, temperature and %Pacific water) but only in the 5-50 m surface water layer. The results suggest that Euchaeta spp. were feeding primarily in the deeper waters and accumulating MMHg through their diet, but they were also acquiring significant levels of inorganic mercury through passive absorption in surface waters.
Themisto spp.
The vertical distribution of Themisto in the water column has been described as unclear and obscure with no defined patterns (61). In the present study, mercury (THg, MMHg and %MMHg) and 813C in Themisto were strongly correlated with water mass properties between 25 to 50 m and 150 to 200 m, suggesting this copepod species is feeding in both surface and deeper waters. These results concur with those of Auel et al. (2003) who demonstrated that Themisto spp. regularly occurred in the surface sample (0-25 m) in the
Greenland Sea (25) and with Percy (1993) who also showed that Themisto libellula occupy the upper 30 m throughout the year in Frobisher Bay, South-eastern Baffin Island, with a clear peak abundance by late August and early September (77). Dalpadado et al.
(2001) found that highest abundance of Themisto libellula was associated with the Polar
Front in the Barents Sea with juveniles prevalent in the surface waters (<25 m) and adult at depths between 100 and 200 m (26). Themisto, depending on its life cycle, is an
52 omnivorous or carnivorous, as juveniles are known to be feeding on phytoplankton and ice algae while adults usually feed on a variety of zooplankton organisms including copepod, pteropod and arrow worms. S13C in Themisto was strongly correlated with temperature and salinity between 25 and 50 m. More depleted 813C values were measured in colder and fresher water (i.e. Fig. 5 a, b, Table 2). Among the three genus studied,
Themisto was found to have the most enriched average 813C (-21.8%o) followed by
Euchaeta (-26.3%o) and Calanus spp. (-30.0%o).
Generally, the relationships observed between THg, MMHg, %MMHg and S13C in all there major zooplankton taxa and water mass properties suggested uptake of inorganic mercury through absorption near surface water (5-25 m for Calanus spp., 5-50 m for
Euchaeta spp. and 25-50 m for Themisto spp.) while uptake of MMHg through diet occurred between 25-50 m and 200 m in Calanus and Themisto and at 5-50 m and 200 m in Euchaeta spp. (See Table 1 in Chapter 4).
Biomagnification factors (BMF's).
Figure 11 illustrates the biomagnification factors (BMF) calculated between Themisto spp. and Calanus spp. and between Euchaeta spp. and Calanus spp. at each sampling locations in the NOW Polynya. Biomagnification factors were calculated between each predatory genus {Themisto spp. and Euchaeta spp.) and Calanus spp. according to the method of Dehn et al. (2006) (30). Based on 815N, BMF was corrected for differences in trophic position between predator and prey:
53 15 15 15 BMF8 N com = ([MMHg] pred./ [MMHg] prey) / (8 N pred./ 5 N prey).
A small number of studies have reported information about biomagnification factors among marine zooplankton in the Arctic. Atwell et al. (27) did not observe any biomagnification of THg with trophic position in Lancaster Sound invertebrates
(BMF<1). They reported THg concentrations of 0.06 ± 0.01 ug/g in both Calanus and
Themisto with 815N values of 10.2 ± 0.6 and 11.6 %o, respectively. Based on their data, the BMF between Themisto and Calanus was calculated to be 0.88 suggesting no biomagnification from Calanus to Themisto. This likely can most be attributed to the fact that only THg and not MMHg was measured. As Themisto is known to be a predator of
Calanus it would be expected that Themisto would have higher MMHg levels. Using the
THg concentrations and 815N values reported by Campbell et al. (50) for a 1997 study conducted in the NOW polynya, a Themisto/Calanus BMF was calculated to be 9.40.
Pazerniuk et al. (2007) reported MMHg BMF values from several regions within Hudson
Bay System. Themisto/Calanus values ranged between 1.26 (Eastern Hudson Bay) and
13.5 (Southern Hudson Strait) and between 2.65 (Eastern Hudson Bay) and 17.6 (Foxe
Channel) Euch/Cal (78). In the present study, MMHg BMF values ranged between 2.75 to 5.64 for Themisto/Calanus and between 4.70 and 7.36 for Euchaeta/Calanus. Highest values were observed at station 131 followed by station 126 (Figure 11). In general, BMF values between Euchaeta/Calanus were higher than those between Themisto/Calanus as
Euchaeta spp. occupy a higher trophic level position as indicated by its 815N values and because Euchaeta spp. is a true carnivorous species of zooplankton (24). Potential ramifications for marine mammals feeding within the NOW are discussed in the following section.
54 Figure 11. Biomagnification factors (BMFs) in the North Water Polynya. Dark grey bars represent BMF between Themisto spp. and Calanus spp. and light grey bars represent BMF between Euchaeta spp. and Calanus spp.
B Themisto/Calanus H Euchaeta/Calanus
127 131 126 118 115 Eastern Arctic locations
55 Implication for marine mammals
The NOW Polynya, being located in the Arctic, is already seeing modifications in its biophysical environment with respect to climate change. Birds and marine mammals are known to be abundant in the polynya for feeding, mating and over wintering purposes
(11,79). Variation in extension and duration of ice cover may alter the seasonal distributions, geographic ranges, patterns of migration, nutritional and reproductive success and thus the abundance of some marine mammal species (80). Along with these possible changes, mercury cycling and uptake by higher trophic level animals may also vary depending on location and time of the year. In this study, zooplankton had higher levels of MMHg in the north-western part of Baffin Bay along the Ellesmere Island (118 and 127). Marine mammals and fishes feeding in these areas could therefore be exposed to higher levels of mercury.
Several satellite tracking studies (81-83) have provided some insight into marine mammal movements in this area of the Arctic. After taking into account the fact that whales generally travel through Baffin Bay and the NOW, it appears that most of the whales occupy the southeast section of our area of study in late summer and fall. Depending on ice conditions, they are also known to spend winter in the NOW polynya. The results from two different aerial surveys over Lancaster Sound and the NOW polynya showed that the majority of beluga whales were located along the shore leads off south-eastern
Devon Island and in the polynya near the mouth of Jones Sound (84). Beluga and narwhals are known to feed on arctic cod off the southeast coast of Devon Island, which in turn feeds mostly on pelagic copepods and amphipods (84). MMHg levels in copepod
56 species were low at our Station 101, nearest to Devon Island and Jones Sound, while in
Themisto, MMHg concentrations were much higher. Therefore, it is possible that mercury uptake by marine mammals could be higher or of greater importance if they are selectively feeding on hyperiid amphipod.
A satellite tracking study conducted on eastern Arctic Bowhead whales (Balaena mysticetus) (85) suggests that these whales are feeding largely on copepods off the east coast of Devon Island near to our two most southerly sampling Stations 101 and 108.
More recently, Laidre et al. (86) examined bowhead whale foraging behaviour in Disko
Bay in late spring between 2001 and 2006 and reported that these bowhead frequented a limited area along the south coast of Disko Bay and had high interannual site fidelity.
Relatively low levels of mercury in zooplankton from these regions and the fact that bowhead are low trophic levels feeders (29,30) translate into low mercury levels in their tissues.
Ringed seals also make great use of the NOW polynya with resident seals spending ~
90% of their time in the eastern parts of its coastal area known for its lighter ice conditions (87). Satellite tracking study conducted in the NOW polynya showed that ringed seals are feeding largely off the Thule area in Greenland (87). Results from the current study suggest that zooplankton from Station 126 did not have particularly high levels of MMHg which may result, therefore, in correspondingly lower levels in ringed seals which feed in this area.
57 It has been known that beluga and especially narwhals are extremely vulnerable to climate change impacts in the Arctic because they have high site fidelity along with restricted habitat preference (88). Indeed, feeding areas and habitat of many Arctic marine species will continue to change over the next few decades which, in turn, may result in increasing dietary mercury exposure in top predator species.
58 References
(1) Barber, D.G.; Marsden, R.; Minnett, P.; Ingram, G.; Fortier, L. Atmosphere- Ocean 2001, 39,163-166. (2) Ingram, R.G.; Bacle, J.; Barber, D.G.; Gratton, Y.; Melling, H. Deep-Sea Research II2002, 49, 4893-4906. (3) Dunbar, M. Arctic 1969, 22, 438-441. (4) Melling, H.; Gratton, Y.; Ingram, G. Atmosphere-Ocean 2001, 39, 301-325. (5) Bacle, J.; Carmack, E. C; Ingram, R.G. Deep Sea Research Part II 2002, 49, 4907-4925. (6) Yao, T.; Tang, C.L. Atmosphere-Ocean 2003, 41, 187-201. (7) Morison, J.; Aagaard, K.; Steele, M. Arctic 2000, 53, 359-371. (8) Hansen, B.; Osterhus, S.; Quadfasel, D. Science 2004, 305, 953-954. (9) Hays, G. C; Richardson, A. J.; Robinson, C. Trends Ecol. Evol. 2005, 20, 337- 344. (10) Mei, Z.-P.; Legendre, L.; Tremblay, J.-E.; Miller, L. A.; Gratton, Y.; Lovejoy, C.; Yager, P. L.; Gosselin, M. Deep-Sea Research 12005, 52, 2301-2314. (11) Stirling, I. Arctic 1980, 33, 303-315. (12) Outridge, P.M.; Macdonald, R.W.; Wang, F.; Stern, G.A.; Dastoor, A.P. Chemistry 2008, In Press. (13) Harada, M. Critical Reviews in Toxicology. 1995, 25, 1-24. (14) Morel, F. M. M.; Kraepiel, A.M.L.; Amyot, M. Annu. Rev. Ecol. Syst. 1998, 29, 543-566. (15) Schroeder, W. H.; Anlauf, K.G.; Barrie, L.A.; Lu, J.Y.; Steffen, A.; Schneeberger, D.R.; Berg, T. Nature 1998, 394, 331-332. (16) Steffen, A.; Schroeder, W.; Macdonald, R.; Poissant, L.; Konoplev, A. Science of The Total Environment 2005, 342, 185-198. (17) Lalonde, J. D.; Poulain, A.J.; Amyot, M. Environmental Science and Technology 2002, 36, 174-178. (18) Berg, T.; Kallenborn, R.; Mano, S. Arct Antarct Alp Res 2004, 36, 283-290. (19) St-Louis, V. L.; Sharp, M. J.; Steffen, A.; May, A.; Barker, J.; Kirk, J. L.; Kelly, D. J. A.; Arnott, S. E.; Keatley, B.; Smol, a. J. P. Environmental Science and Technology 2005, 39, 2686-2701. (20) Leitch, D. R.; Carrie, J.; Lean, D.; Macdonald, R.W.; Stern, G.A.; Wang, F. Science of the Total Environment 2007, 373, 178-195. (21) Loseto, L.L.; Stern, G.A.; Deibel, D.; Connelly, T.L.; Prokopowicz, A.; Lean, D.R.S.; Fortier, L.; Feguson, S.H. Journal of Marine Systems 2007, (In Press). (22) Deutch B.; Pedersen, D. J.; Asmund, H.S.; M0ller, G.P.; Hansen, J.C. The Science of The Total Environment 2006, 370, 372-381. (23) Ritterhoff, J.; Zauke, G.P. The Science of the Total Environment 1997, 199, 255- 270. (24) Skarra, H.; Kaartvedt, S. Marine Ecology Progress Series 2003, 249, 215-222. (25) Auel, H.; Werner, I. Journal of experimental marine biology and ecology 2003, 296, 183-197.
59 (26) Dalpado, P.; Borkner, N.; Bogstad, B.; Mehl, S. Journal of Marine Science 2001, 58, 876-895. (27) Atwell, L.; Hobson, K.A.; Welch, H.E. Can. J. Fish. Aquat. Sci. 1998, 55, 1114- 1121. (28) Hobson, K.A.; Fisk, A.; Kamovsky, N.; Hoist, M.; Gagnon, J.M.; Fortier, M. Deep-Sean Research II2002, 5131-5150. (29) Hoekstra, P.F.; Dehn, L.A.; George, J.C.; Solomon, K.R.; Muir, D.C.G.; O'Hara, T.M. Can. J. Zool. 2002, 80, 223-231. (30) Dehn, L.-A.; Follmann, E.H.; Thomas, D.L.; Sheffield, G.G.; Rosa, C; Duffy, L.K.; O'Hara, T.M. Science of the Total Environment 2006, 362, 103-123. (31) Burreau, S.; Zebuhr, Y.; Broman, D.; Ishaq, R. Science of the Total Environment 2006, In Press. (32) Dehn, L.-A.; Follmann, E.H.; Rosa, C; Duffy, L.K.; Thomas, D.L.; Bratton, G.R.; Taylor, R.J.; O'Hara, T.M. Marine Pollution Bulletin 2006, 52, 301-319. (33) Grasshoff, K. 1999, 600 pp. (34) Uthe, J. F.; Solomon, J.; Grift., N. Journal - Association of Official Analytical Chemists 1972, 55, 583-589. (35) Cai, Y. International Journal of Environment and Analytical Chemistry 1997, 68, 331-345. (36) Murry, B.A.; Farrell, J.M.; Teece, M.A.; Smyntek, P.M. Can. J. Fish. Aquat. Sci 2006,63,2167-2172. (37) Falkner K.K.; O'Brien M.C.; Melling H.; Carmack E.C.; McLaughlin F.A.; Munchow A.; Jones, E.P. JGR Biogeosciences special issue on the Arctic Freshwater Cycle 2006, 50 pp. (38) Jansson, M. Hydrobiologia 1988, 170, 177-189. (39) Muench, R.D. Baffin Bay-North Water Project Scientific Report No. 1. Arctic Institute of North America, Washington, D. C. 1971,150 p. (40) Sarmiento, J.L.; Slater, R.; Barber, R.; Bopp, L.; Doney, S.C.; Hirst, A.C.; Kleypas, J.; Matear, R.; Mikolajewicz, U.; Monfray, P.; Soldatov, V.; Spall, S.A.; Stouffer, R. Global Biogeochemical Cycles 2004, 18, doi:10.1029/2003GB002134. (41) Tremblay, J.-E.; Payne, C; Price, N.M.; Gratton, Y; Carmack, E.C. Journal of Geophysical Research 2002, 107,doi:103 110.1029/2000JC000595. (42) Yamamoto-Kawai, M.; Carmack, E.; McLaughlin, F. Nature 2006, 443, 43. (43) Falck, E. Polar Research 2001,20,193-200. (44) Nicholson, L., Sharp, M. and Fisher D. 3rd Annual ArcticNet Scientific Meeting. December 12-15, 2006. Victoria, Brithish Columbia. 2006,78. (45) Wang, L.; Sharp, M.; Rivard, B.; Marshall, S.; Burges, a. D. Geophysical Research Letters 2005, 32, doi:10.1029/2005GL023962. (46) Boon, S.; Sharp, M. Geophysical Research Letters 2003, 30, 1916, doi:1910.1029/2003GL018034. (47) Tranter, M.; Brown, G.; Raiswell, R.; Sharp, M.; Gurnell, a. A. Journal of Glaciology 1993, 39, 573-581. (48) Wynn, P. M.; Hodson, A.; Heaton, T. Biogeochemistry 2006, 78, 173-193. (49) Hooper, R. P. (2003), Diagnostic tools for mixing models of stream water chemistry, Water Resour. Res., 39(3), 1055, doi:10.1029/2002WR001528
60 Campbell, L. M., Norstrom, R.J., Hobson, K., Muir, D.C.G., Backrus, S., Fisk, A.T. Science of the Total Environment 2005, 351-352, 247-263. Kainz, M.; Telmer, K.; Mazumder, A. Science of the Total Environment 2006, 368, 271-282. Braune, B.M.; Outridge, P.M.; Fisk, A.T.; Muir, D.C.G.; Helm, P.A.; Hobbs, K.; Hoekstra; P.F.; Kuzyk, Z.A.; Kwan, M.; Letcher, R.J. Science of The Total Environment 2005, 351-352, 4-56. Greene, C.H.; Landry, M.R. Ecology 1985, 66, 1408-1416. Kainz M.; Lucotte M.; Parrish, C.C. Can. J. Fish. Aquat. Sci. 2002, 59, 1606- 1615. Zauke, G. P.; Petri, G.; Ritterhoff, J.; Meurs, H.G. Senckenbergiana maritima 1996,27,207-214. Mayzaud P.; Errhiff A.; Bedo A. Journal of Marine Systems 1998,17, 391-410. Rau, G.J.H.; Mearns, A.J.; Young, D.R.; Olson, R.J.; Schafer, H.A.; Kaplin, I.R. Ecology 1983, 64, 1314-1318. Andersson, A.; Rudehall, A. Marine Ecology Progress Series 1993, 95, 133-139. Schell, D.M.; Barnett, B.A.; Vinette, K.A. Marine ecology progress series 1998, 162,11-23. Wim, CM.; Breteler, K.; Grice, K.; Schouten, S.; Kloosterhuis, H.T.; Damste, J.S. Marine ecology progress series 2002, 240, 195-204. Longhurst, A.; Sameoto, D.; Herman, A. Journal of Plankton Research 1984, 6, 137-168. Daase, M.; Eiane, K. Polar Biology 2007, 30, 969-981. Prokopowicz, A.; Fortier, L. Polish Polar Research 2002, 23, 241-252. Yamaguchi, A.; Dceda, T.; Watanabe, Y.; Ishizaka, J. Zoological Studies 2004,43, 475-485. Bonnet, D.; Frid, C. ICES Journal of Marine Science 2004, 61, 485-491. Schauer, U.; Fahrbach, E.; Osterhus, S. Journal of Geophysical Research 2004, 109, C06026, doi:06010.01029/02003JC001823. Herman, A.W. Limnology and Oceanography 1983,28, 709-719. Visser, A.W.; Jonasdottir, S. H. Fisheries Oceanography 1999, 8, 100-106. Sato, M.; Sasaki, H.; Fukuchib, M. Journal of Marine Systems 2002, 38, 165-174. Pedersen, S.A.; Ribergaard, M.H.; Simonsen, C.S. Journal of Marine Systems 2005, 56, 85. Mysak, L.A.; F.Huang Journal of Physical Oceanography 1992, 22, 596-608. Naidu, P.D. Global and Planetary Change 2004, 40, 3-4, 285-293. Kaartvedt, S.; Trine, D.; Espen, B.; Tom, V. Journal of Plankton Research 2002, 24, 155-158. Vestheim, H.; Kaartvedt, S.; Edvardsen, B. Journal of Plankton Research 2004, 27. Lagadeuc, Y.; Boute, M.; Dodson, J. J. Journal of Plankton Research 1997, 19, 1183-1204. Jones, E.P.; Anderson, L.G., Swift, J.H. Geophysical Research Letters 1998, 25, 765-768. Percy, J. Polar Biology 1993, 13, 131-139. Pazerniuk, M.A. Master of Science Thesis - University of Manitoba 2007, 1-157.
61 (79) Stirling, I. Journal of Marine Systems 1997, 10, 9-21. (80) DeMaster, D.P.; Tynan, C.T. Arctic 1997, 50, 308-322. (81) Richard, P.R.; Orr, J.R.; Dietz, R.; Dueck, L. Arctic 1998, 51, 1-4. (82) Richard, P.; Heide-Jorgensen, M.P.; Orr, J.; Dietz, R.; Smith, T. G. Arctic 2001, 54,207-222. (83) Richard, P.; Heide-Jorgensen, M.P.; St-Aubin, D. Arctic 1998, 51, 5-16. (84) Welch H.E.; Crawford, R.E.; Hop H. Arctic 1993, 46, 331-339. (85) Heide-Jorgensen, M. P.; Laidre, K. L.; Wiig, O.; Jensen, M. V.; Dueck, L.; Schmidt, H.C. Arctic 2003, 56, 21-31. (86) Laidre, K.L.; Heide-Jorgensen, M.P.; Nielsen, T.G. Mar. Ecol. Prog. Ser. 2007, 346, 285-297. (87) Born, E.W.; Teilmann, J.; Acquarone, M.; Riget, F.F. Arctic 2004, 57,129-142. (88) Heide-Jorgensen, M.P.; Dietz, R.; Laidre, K.L.; Richard, P.; Orr, J.; Schmidt, H.C. Can. J. Zool. 2003, 81, 1298-1305.
62 CHAPTER 3
Relationships between Mercury, 813C and Water Masses in Marine Pelagic Zooplankton of the Mackenzie Shelf, Beaufort Sea, in September and October 2005-2006.
By Corinne Pomerleau
63 Abstract
This study was designed to investigate relationships between total mercury (THg), monomethyl mercury (MMHg) and stable isotopes (813C and 515N) in Arctic marine pelagic zooplankton with water mass characteristics (salinity, temperature, 5180 and nutrients) for the Mackenzie Shelf- Amundsen Gulf area. Samples were collected as part of the ArcticNet cruises on the CCGS Amundsen in late summer and early fall of 2005 and 2006. In general, water in this region was composed of a fresher polar mixed layer
(surface to 50 m), a two-component Pacific halocline (upper -50-100 m and lower ~ 100-
200 m) and a deep Atlantic water layer (>200 m). Surface water was fresher in the western part of the Mackenzie Shelf and was strongly linked to influence of the
Mackenzie River. Temperature and THg were found to be strongly positively correlated in surface waters while THg was also found to be negatively correlated with salinity and nitrite concentrations suggesting that the higher THg concentrations in zooplankton were associated with the delivery of Hg originating from the Mackenzie River. The relationships observed between THg, MMHg, %MMHg in THg and 813C in all three major zooplankton taxa and water mass properties suggested feeding and uptake of inorganic Hg through absorption near surface water (5-50 m for Themisto and Euchaeta and 5-25 m for Calanus) and feeding and uptake of MMHg through diet at or near 200 m.
Higher THg concentrations were associated with fresher water (low salinity and warmer temperature) and with large fractions of both meteoric water and sea-ice melt. This suggests that in the western Arctic, inorganic Hg uptake in zooplankton via absorption near surface water was largely driven by freshwater inputs into the system. Hg uptake by higher trophic level animals as well as Hg cycling may also vary depending on location
64 and time of the year. Marine mammals living or passing through that region could be exposed to higher levels of Hg if feeding off the Mackenzie River as zooplankton had higher levels of MMHg along that transect.
Introduction
The most recent decade in the Arctic has been largely characterised by significant changes in sea ice cover, ocean structure and freshwater budget. The sea ice extent in
September 2007 was the minimum ever observed since the beginning of the satellite monitoring in 1979, with an unprecedented series of extreme ice extent minima occurring in 2005 and 2007 (NSIDC. 2007b). Biogeochemical cycles and contaminants processes and transport are thought to be largely influenced by those primary and rapid climate changes (1-3). Study of lower tropic level pelagic animals (zooplankton) is crucial to understanding the consequences of these changes as they are keystone component in arctic food web being the main linkage between primary production and higher predators such as fishes, birds and marine mammals. These low trophic level organisms are most dependant on the variation in water masses and react quickly to changes in their environment. Advection, changes in runoff, glacial melt, sedimentation and freshwater input are processes known to affect zooplankton structure and community (4). Study of biological markers such as stable isotopes of carbon and nitrogen, along with several types of contaminants (e.g. Hg), can also be used as tracers of oceanographic processes
For the Mackenzie Delta and the Southeastern Beaufort Sea, physical forcing mechanisms and hydrographic characteristics of the waters transiting though Bering
65 Strait and over the Chukchi and Beaufort shelves are essential drivers of the productivity of this ecosystem. Inflow from the Mackenzie River during summer dominates the surface water inputs of nutrients, organic carbon and sediments to the estuary. Salinity and temperature on the shelf depend on offshore water masses by river inflow, ice melting and freezing, solar insulation and air-sea exchange (5). Usually, freshet begins in early May and peaks from the third week of May to the first week of July (1). The water in this region consists primarily of a Polar-Mixed Layer (0-50 m), the Pacific Halocline
(50-200 m) and the Atlantic Water layer at the bottom (>200 m) (6).The outer shelf and slope are under the influence of the Beaufort Gyre, which is forced by the primarily northeast winds that induce a westward flow tendency and upwelling. In contrast, the flow reverses along the continental slope below the first 50 m (Beaufort Undercurrent) and carries Pacific and Atlantic origin waters eastward (See Figure 1) (7).
Hg is one of the leading contaminants of concern in the Arctic. The Mackenzie River
Basin has been shown to yield high Hg loads to the Mackenzie Delta and the Eastern
Beaufort Sea (8,9). Produced mainly by microbial methylation of inorganic Hg in aquatic environments, mono-methylmercury (MMHg), a potent neurotoxin, bioaccumulates up through marine food webs where it can reach substantial levels in top predators such as beluga whales {Delphinapterus leucas), ringed seals (Phoca hispida) and polar bears
(Ursus maritimus) (10). Hg levels in the liver of Beaufort Sea beluga have tripled since the late 1980s (16).
66 Within-ecosystem processes are thought to play a critical role in the toxicity and distribution of Hg in the arctic (11). For example, riverine Hg discharge, direct terrestrial
Hg input from melted permafrost and coastal erosion, oceanic Hg transport (9), sea ice
loss, marine mammal habitat, feeding patterns and food web structures (12) are thought to result in increasing Hg exposure to top trophic level species. Atmospheric deposition of
Hg during spring mercury depletion events (MDE's) was thought to be the dominate
source of Hg to the Arctic (13). However, it has recently been demonstrated that more
than half of the Hg deposited during the MDE's is photoreduced and is then rapidly reemitted back into the atmosphere (14). Outridge et al. (2008) recently suggested that
the rate of biological uptake and trophic transfer from the large abiotic MeHg reservoir
may be a key regulator through processes such as food-web ecology, ocean
biogeochemistry and animal physiology and ecology (15).
Stable isotopes of nitrogen (815N) are used to determine trophic position relative to
contaminant concentrations and biomagnification (18-20) while isotope ratios of carbon
(813C) in consumer tissues and potential prey is a useful tool in assigning pathways of
energy flow and for tracing primary production (20,21). Carbon is also employed to
differentiate inshore or benthic prey feeding from offshore or pelagic feeding type
organisms (22). Thus, the increasing dominance of terrigenous sources of carbon coming
from the Mackenzie River through the eastern Beaufort Sea could be traced using 8 C.
A well known isotopic gradient of depleted 13C signal along a west to east transect has
been observed in zooplankton, benthic organisms and bowhead whale baleen along the
shelf from Alaska to the western Beaufort Sea (23-25). Dunton et al. (2006) pointed out
67 that this strong decreasing gradient along the western Beaufort Sea coast followed the path of the Beaufort Undercurrent, which is mainly composed of the warmer Bering
Strait outflow (7).
The main goal of this study was to determine the spatial and interspecific (inter-specie) variability of 813C and 815N and Hg (total (THg) and methyl (MMHg)) among four keystone zooplankton genus. We assessed whether there was a trend in 513C values within the Mackenzie Shelf and throughout the Amundsen Gulf among a broad range of zooplankton taxa. Lastly, we determined how the biology of the different zooplankton genus, Calanus spp. Themisto spp., Euchaeta spp. and Sagitta spp. is linked with Hg uptake and 813C. We used measurements of several oceanographic parameters including temperature, salinity, 5180 and nutrients to help distinguish water masses.
Material and Methods
Sampling was performed onboard the research Icebreaker CCGS Amundsen during late summer cruises in 2005 (1-15 September) and 2006 (28 September - 19 October) in the western Arctic (Figure 1). The study region (120 X 530 km) is enclosed by the
Mackenzie River to the south, the Amundsen Gulf to the east, the Beaufort Sea to the north and the Mackenzie Canyon to the west (6). The Mackenzie Shelf is characterised by an annual inflow of 333 km'yr"1 of freshwater delivered by the Mackenzie River together with a sediment load of 127 x 106 Mtyr"1 causing this continental shelf to be the most estuarine one across the Arctic (1,26,27).
68 Water collection and analysis
Water samples were collected with 12-L Niskin bottles attached to a rosette sampler equipped with Seabird 911+ CTD (Sea-Bird Electronics, Inc.) and analysed for salinity,
8180 isotope and Hg at 8 stations and for nutrient at 20 stations with an average of 10
depths per station (surface, 2.5, 5, 7.5, 10, 25, 50 and 200 meters). See Chapter 2 Material
and Methods section for more details.
The water masses of the Arctic Ocean shelf regions, such as the Mackenzie shelf area, are
significantly influenced by sea-ice processes and riverine inputs. The 8180 (180/160 ratio)
and salinity of a water sample are usually used to differentiate water sources as river
water and sea ice are highly depleted (more negative) in oxygen relative to marine waters
(29). We considered a mixture of three primary types of water present in the Mackenzie
estuary; a saline end member (polar mixed layer (PML)), a source of meteoric fresh water
(MW) which is essentially (~95%) composed of the Mackenzie River runoff and a small
amount of precipitation water (-5%), and a source/sink of brackish water (sea ice melt
(SIM)). The measurements of two conservative properties (salinity and 5180) in the above
noted end members is required if we are to determine the composition of a given water
sample. The fraction of each of the end members was calculated using the method
described by Macdonald et al. (1995) (30).
69 Figure 1. Sampling locations on the Mackenzie Shelf-Beaufort Sea region. Red circles represent stations where zooplankton were collected, red circles with a green border represent Hg water collection stations and the black dots represent the CTD stations.
rrn
7TM
72°N
71'N
7WM
W*
68°N 135°W fSS'W ns'w f2ffW
70 FPML + FMW + FSIM = 1
FPMLSPML+ FMWSMW+ FSIMSSIM = 1
FPML8PML+ FMW5MW+ FSIMSSIM — 1
where the subscripts refer to the three primary water types, F is the fraction of each primary water type, S and 8 correspond respectively to salinity and 81 O compositions.
We used the following end member values for our calculations (30);
PML: 33.1 (Salinity) and -1.1 (S180)
SIM: 6 (Salinity) and -0.43 (S180)
MW: 0.15 (Salinity) and -20.3 (S180)
Zooplankton collection and analysis
Zooplankton samples were collected at 8 stations in 2005 and 10 stations in 2006 with a vertically towed Monster net, a set of 4 adjacent 1-m2 frame nets (mesh size 200 um &
500 um), from near the bottom to the surface and by trawling an oblique rectangular mid- water trawl (mesh size 1600 um) or an oblique Tucker net (mesh size 2x500 um) in the surface layer from 100 m depth to the surface. Samples were placed into 30 ml plastic vials and/or whirl-pak bags and were kept frozen at -20°C until further analysis for THg and MMHg. Representative sub-samples of individual zooplankton genera were placed in
4 ml glass vials for analysis of 515N, and 813C. Three keystone zooplankton genus were included in this study: the herbivorous copepod Calanus spp. (mostly adult Calanus hyperboreus), the hyperiid amphipod Themisto spp. (mostly adult Themisto libelluld) and
71 carnivorous copepod Euchaeta spp. See the Material and Methods section in Chapter 2 for more details on THg, MMHg and stable isotopes analyses.
Biomagnification factors (BMF) were calculated between each predatory genus
{Themisto spp. and Euchaeta spp.) and Calanus spp. according to the method of Dehn et al. (2006) (17). Based on 815N, BMF was corrected for differences in trophic position between predator and prey:
15 15 15 BMF8 NCorr. = ([MMHg] pred/ [MMHg] prey) / (8 N pred/ 8 N prey).
Statistical Analysis
To test for a longitudinal and/or a latitudinal gradient in 513C among the 4 most ubiquitous genus which include Calanus spp., Euchaeta spp., Sagitta spp. and Themisto spp., we used an ANCOVA with 813C as the dependent variable, genus as the factor and longitude and latitude as the covariate variable. For environmental variables explaining
Hg concentration, a General Linear Model (GLM estimate model) using THg as the dependent variable coupled with station, year and station*year as the independent variables was used to assess the effect of station and/or year on THg. Since no significant effect was found, the 2005 and 2006 Hg data were pooled together. A paired t-test was employed to control for sample sites and to test for significant difference between 815N in the three genus. A Principal component analysis (PCA) was used to identify a smaller set of uncorrelated factors (orthogonal or independent) among the abiotic parameters and
THg levels measured in the Mackenzie shelf area at several depths. To understand
72 environmental variables responsible for variations in Hg and carbon, several least squares
linear regressions were used to determine correlation between THg, MMHg, %MMHg
and 813C with all the abiotic parameters including position (latitude and longitude), temperature, 8180, salinity, percent Pacific water, nutrients (nitrate, nitrite, phosphate,
silicate, ratio N:P). Statistical tests were performed using SYSTAT Software version
11.0 with significance level p<0.05. All descriptive variables are given as mean +/-
standard error. The program Ocean Data View version 3.3.1 2007 was used to create
surface and section maps.
Results and Discussion
Mercury levels in zooplankton
Table 1 summarizes THg and MMHg levels, %MMHg in THg and stable isotopes of
carbon and nitrogen in Calanus, Euchaeta and Themisto at 10 different stations. Calanus
had the lowest THg ± S.E. concentrations among the three genus with a mean level of
23.3 ± 5.6 ng/g (dw). Themisto and Euchaeta had mean concentrations of 65.5 ± 21.1
and 81.3 ± 31.3 ng/g (dw), respectively. Similarly, Calanus had the lowest MMHg levels
with a mean concentration of 10.1 ± 3.5 ng/g (dw). Themisto and Euchaeta had mean
concentrations of 33.2 ± 14.4 and 44.3 ± 2.4 ng/g (dw), respectively. The percentage of
MMHg in THg ranged from 44.8 ± 1.9 % in Calanus to 52.0 ± 1.3 % and 54.9 ± 1.0 % in
Themisto and Euchaeta, respectively. Significant linear relationships were found to occur
between THg, MMHg, %MMHg and 513C among genus. THg and MMHg were strongly
positively correlated in both Themisto (^=0.84, p=0.03) and Euchaeta (1^=0.93, p=0.002)
73 Table 1. Total mercury (THg), methyl mercury (MMHg), percent methyl mercury in •t'J 1 C THg (%MMHg), 8 C and 5 N values for Calanus spp., Euchaeta spp. and Themisto spp. at the 10 sampling stations on the Mackenzie Shelf-Beaufort Sea region (mean ± standard error).
Station id. Taxonomic Group - Genus THg (ng/g dw) ± SE MMHg (ng/g dw) ± SE %MMHg 6,3C (%.) ± SE 515N (%,) ± SE 403 Copepod Calanoid - Calanus spp. 16.2 ±0.8 5.1 ±0.4 31.48 -29.42 ±0.16 9.18 ±0.43 Copepod Calanoid - Euchaeta spp 62.1 ±6.8 36.0 ±4.2 57.97 -28.23 ± 0.44 12.36 ±0.65 Hyperiid Amphipod - Themisto spp 47.1 ± 3.8 26.0 ± 0.8 55.30 -27.54 ± 0.44 12.17 ±0.72 405 Copepod Calanoid - Calanus spp. 20.0 ± 2.0 9.0 ±0.1 45.00 -27.06 ±0.18 9.81 ± 0.24 Copepod Calanoid - Euchaeta spp 48.1 ±3.6 28.3 ± 0.0 58.84 -28.67 ± 0.26 13.20 ±0.69 Hyperiid Amphipod - Themisto spp 47.9 ±5.5 27.3 ± 2.8 56.99 -25.59 ± 0.44 11.84 ±0.48 407 Copepod Calanoid - Calanus spp. - - - - - Copepod Calanoid - Euchaeta spp 63.7 ± 6.8 - - -29.12 ±0.21 11.99 ±0.14 Hyperiid Amphipod - Themisto spp 55.7 ± 0.2 - - -22.83 ± 0.22 11.62 ±0.15 408 Copepod Calanoid - Calanus spp. 21.5 ±1.0 14.1 ±0.2 65.58 -32.72 ±0.16 10.72 ±0.13 Copepod Calanoid - Euchaeta spp 75.9 ±0.1 32.1 ± 7.3 42.42 -28.79 ± 0.48 12.36 ±0.42 Hyperiid Amphipod - Themisto spp 72.1 ±11.1 37.4 ± 2.2 51.87 -27.73 ± 0.32 12.15 ±0.26 420 Copepod Calanoid - Calanus spp. - - - -27.96 ±0.13 10.49 ±0.17 Copepod Calanoid - Euchaeta spp - - - -25.42 ±0.13 12.56 ±0.17 Hyperiid Amphipod - Themisto spp 84.0 ± 6.9 43.9 ± 7.0 52.63 -21.21 ±0.13 12.48 ±0.17 421 Copepod Calanoid - Calanus spp. 26.6 ± 5.0 18.9 ±2.1 71.05 -29.23 ±0.16 10.72 ±0.13 Copepod Calanoid - Euchaeta spp 105.9 ±9.7 47.5 ± 5.4 44.85 -28.50 ±0.16 13.75 ±0.13 Hyperiid Amphipod - Themisto spp 154.6 ±29.6 - - -30.29 ± 0.24 9.56 ± 0.26 424 Copepod Calanoid - Calanus spp. 34.7 ± 3.0 14.1 ±0.6 40.63 -29.92 ±0.16 10.30 ±0.13 Copepod Calanoid - Euchaeta spp 107.8 57.0 ± 0.6 52.88 -29.34 ±0.16 12.79 ±0.13 Hyperiid Amphipod - Themisto spp 130.0 ±17.8 - - - - 435 Copepod Calanoid - Calanus spp. 23.7 ±1.6 8.1 ±0.4 34.18 -35.05 ± 0.21 11.44 ±0.57 Copepod Calanoid - Euchaeta spp 114.7 ±0.8 62.4 ±1.2 54.40 -27.45 ±0.16 13.80 ±0.13 Hyperiid Amphipod - Themisto spp 115.2 ±28.9 40.8 ±4.2 35.42 -21.57 ±0.16 12.26 ±0.43 434 Copepod Calanoid - Calanus spp. 19.8 ±1.8 10.2 ±0.6 51.52 -29.92 ±0.16 10.18 ±0.48 Copepod Calanoid - Euchaeta spp 52.8 - - - - Hyperiid Amphipod - Themisto spp 51.7 ±3.4 - - -28.22 ± 0.32 11.81 ±0.26 436 Copepod Calanoid - Calanus spp. 24.1 ±1.6 0.0149 ± 0.0061 61.83 -31.44 ±0.35 10.85 ±0.26 Copepod Calanoid - Euchaeta spp 49.4 ± 0.9 0.0297 ± 0.0014 60.12 -25.40 ± 0.22 13.50 ±0.22 Hyperiid Amphipod - Themisto spp 70.0 ± 4.6 0.0338 ± 0.0002 48.29 -25.72 ± 0.36 12.38 ±0.34
74 which indicated that individuals having more THg also have higher MMHg levels.
Interestingly, THg and %MMHg were found to be strongly negatively correlated together in Themisto (^=0.83, p=0.03) suggesting that these genus acquired significant levels of
Hg through passive absorption from the surrounding waters. %MMHg in Themisto was strongly negatively correlated with 813C (1^=0.91, p=0.01). THg concentrations in zooplankton are generally related to their trophic position with predatory genus having higher proportion of MMHg (34). Euchaeta and Themisto are carnivorous zooplankton genus which explains why they have both higher MMHg and %MMHg in comparison to the herbivorous Calanus. As indicated by their 815N, they both occupied higher trophic positions with mean values of 13.1 ± 1.2 and 11.7 ± 1.5 %o in Euchaeta and Themisto, respectively, compared to 10.4 ± 0.8 %o in Calanus. Results from a paired t-test revealed that 5 5N was significantly different between Calanus and Euchaeta (t=-11.5, p=0.000) and between Calanus and Themisto (t=-7.5, p=0.000). While MMHg levels in zooplankton are thought to increase with body size, Kainz et al. (35) demonstrated that
MMHg concentrations in zooplankton were linked to both habitat and spatial distribution in the water column.
Figure 2 and 3 illustrate the observed spatial variation of concentration of THg, MMHg concentrations and %MMHg in all three taxa along with salinity, 8180 and the fraction of meteoric water (FMW) in surface waters (0-10 m). It is evident from the latter water properties that the surface water is fresher in the western part of the Mackenzie Shelf and was strongly linked to influence of the Mackenzie River. THg and MMHg concentrations
75 Figure 2. Spatial patterns of a) THg in Calanus spp., b) THg in Themisto spp., c) THg in Euchaeta spp., d) MMHg in Calanus spp., e) MMHg in Themisto spp. and f) MMHg in Euchaeta spp. on the Mackenzie Shelf-Beaufort Sea region.
(a) | (b)
(d) (e)
76 Figure 3. Spatial patterns of a) %MMHg in THg in Calanus spp., b) %MMHg in THg Themisto spp., c) %MMHg in THg in Euchaeta spp., d) Salinity 0-10m, e) 5180 0-10m and f) Fraction of meteoric water (FMW) 0-10m on the Mackenzie Shelf-Beaufort Sea region.
c (a) (b) ( ) •
(d) (e) (f)
77 in Calanus, Themisto and Euchaeta were the highest in the western section of the area of study and concentrations decreased eastward (Fig. 2 a-f). %MMHg in Calanus peaked at station 421 and in Northern Franklin Bay (stn 408) (Fig. 3 a) and gradually declined both to the east and west. Conversely, the highest %MMHg in Themisto and Euchaeta was observed in eastern Amundsen Gulf (Fig. 3 b-c).
Carbon and Nitrogen in zooplankton
Throughout the study area, the most depleted average 813C occurred in Calanus spp. with a mean value of -28.6 ± 2.8 %o followed by Euchaeta spp. with a mean value of -26.9 ±
1 "X 1.6 %o. Themisto spp. and Sagitta spp. had mean 5 C values of -25.8 ±1.8 and -25.6 ±
3.1 %o, respectively. Saupe et al. (23) reported a value of -26.7 %o in Copepod calanoids in the Southern Canadian Beaufort Sea and Schell et al. (21) values of -25.6 %o in
Calanus spp. and -23.8 %o in Sagitta spp. for that same area.
Contrary to the finding by Saupe et al. (23) and, more recently by Stern et al. (8), the
ANCOVA results for all taxa included in this study revealed no east to west gradient of
813C, with less depleted more positive values toward the west (Table 2a). No significant correlation was observed with latitude along either of the two north to south transects
(Table 2b). As was also reported by Schell et al. (25), the most depleted 513C values in the present study were observed in the copepods sampled near the mouth of the
Mackenzie River. These low 813C signals could be explained by the freshwater inputs of terrigenous organic matters by the Mackenzie River.
78 Table 2. Results from a) the ANCOVA on longitudinal gradient and b) the ANCOVA on latitudinal gradient in 813C among the 4 most ubiquitous genus (Calanus spp., Euchaeta spp., Sagitta spp. and Themisto spp.) on the Mackenzie Shelf-Beaufort Sea region. a)
Source Sum-of-Squares df Mean-Square F-ratio P Genus 3.354 3 1.118 0.196 0.898 Longitude 14.25 1 14.25 2.505 0.119 Genus * Longitude 2.827 3 0.942 0.166 0.919 Error 324.314 57 5.69 b)
Source Sum-of-Squares df Mean-Square F-ratio P Genus 3.140 3 1.047 0.178 0.911 Latitude 2.678 1 2.678 0.454 0.503 Genus * Latitude 3.224 3 1.075 0.182 0.908 Error 335.923 57 5.893
79 Figure 4. Mean 813C values ± SE of all zooplankton genus pooled at each station (n=14) against longitude across the Mackenzie Shelf-Beaufort Sea region.
f, r2 = 0.30 : t f *[ #
* ; 1
i i i i -135 -132 -129 -126 -123 -120 Longitude (dd)
80 Calanus spp. is the true herbivore genus in this study while Sagitta spp., Euchaeta spp. and Themisto spp. are considered planktonic carnivores. The relative depletion in 513C in
Calanus spp. to the other taxa may be due to its higher percentage of lipid carbon by weight (20). S13C was negatively correlated to the lipid content as lipids are depleted in
813C compared to protein and the carbohydrate fractions (36). 813C values in zooplankton may exhibit a small seasonal difference due to seasonal change in lipids but all samples were collected at the same time of the year in this study (37). Herbivorous zooplankton such as Calanus spp. feed on two main sources of marine particulate organic matter
(POM), phytoplankton and ice algae. Phytoplankton had a more depleted 813C value whereas ice algae is by definition enriched in carbon (18). Since 6l3C in POM was not measured, the base value of 813C in the different sections of the study regions is unknown. Thus, some of the variability observed in the enrichment versus depletion of the 813C in zooplankton could result from some the variability of the food sources
assimilated. Across the entire study region each genus was positioned within a single
trophic level. Mean values of 8I5N in Calanus, Themisto and Euchaeta spp. were 10.4 ±
0.8 %o, 11.7 ± 1.5 %o and 13.1 ± 1.2 %o, respectively (Table 1). Conversely, the 815N value for Sagitta (12.2 ± 2.3 %o) suggested that this specie spans two trophic levels. The
true carnivorous type of diet of Euchaeta spp. positions it at a higher trophic level than
Themisto spp. which is known to be omnivorous (90). Figure 5 shows the predator - prey
relationship between zooplankton across the Mackenzie Shelf-Beaufort Sea region.
81 Figure 5. Relationship between 813C and 815N for zooplankton across the Mackenzie Shelf-Beaufort Sea region.
16
15 - 408
14 435 4^ » 43^ ^ 4^3 13 A-M 424 • r 421 435 408 A r • D 436 405 Z 11 420 u> D 407 D 4*5 lb 10
9 434 4^ 8
7 - Freshwater Marine 6 " ! I -36 -34 -32 -30 -28 -26 -24 -22 -20 513C (%o) • Chaetognatha - Sagftfa spp. D Copepod Calanoid - Cafanus spp. ACopepod Calanoid - Euchaeta spp. X Hyperiidea Amphipod - Themfsto spp.
82 Zooplankton collected along the Mackenzie Shelf was clearly influenced by the freshwater from the Mackenzie River. Less depleted 513C values were observed at a few stations in Sagitta spp. and in Themisto spp. From the spatial distribution of the four genus shown in Figure 5, it is clear that Calanus spp. were feeding on a terrestrial source of particulate organic matter (more depleted 815N and 813C) whereas the three other genus were predators. The position of Euchaeta spp. at different stations indicates that they were primarily a predator of Calanus spp. while Sagitta spp. and Themisto spp. alternate between a marine predator and/or terrestrial at some stations. Based on the observed range of 813C values (-30.29 to -21.21 %o). Themisto spp. seemed to feed on a wide range of prey species
Hydrography
As noted previously in the Methods section, the sampling area was divided into two latitudinal and one longitudinal transects (Figure 6). Figures 7 (a-i) to 9 (a-g) show the temperature, salinity, nitrite, nitrate, phosphate, silicate and the N:P ratio contour plots for each transect. Water THg concentrations, where available, were superimposed onto each of the contour maps. Silicate was selected because it is the nutrient that exhibits the largest difference between Pacific and Atlantic waters (38). The Mackenzie River has been shown to exert a strong freshwater influence on the Mackenzie shelf waters as it discharges to a relatively small offshore area during the summer compared to other large arctic rivers (39). This influence generally limits vertical mixing across the shelf and
83 Figure 6. Mackenzie Shelf - Eastern Beaufort Sea transects: 1: 421-434, 2: 410-420, 3: 403-408. Red star represents station 436 in Franklin Bay.
74'M
73°H
72°N
71°N
70'N
•9°*
$*°N f35°l* 130°W 1iS°W 120°W
84 Table 3. Summary table of salinity, 8180, temperature, THg levels, nitrite, nitrate, phosphate and silicate at surface, 25, 50, 100 and 200 m at each of the 9 stations on the Mackenzie Shelf-Beaufort Sea region (Mean ± SE). 16 Station Latitude (dd) Longitude (dd) Depth (m) Salinity (psu) 5 Q(%.) T(°C) THg(ng/L) NQ2(uM) NQ3(UM) PQ4(uM) Si(uM) 403 70.101 -120.096 Surface 29.57 ±0.0005 -3.02 ±0.07 2.13 0.10 0.00 0.60 2.75 25 31.53 ±0.0005 -2.51 ±0.07 -0.75 0.18 1.95 0.87 6.56 50 32.30 ±0.0006 -2.06 ±0.07 -1.43 0.40 10.13 1.34 21.45 100 32.95 ±0.0002 -1.54 0.10 15.65 1.59 30.12 200 34.23 ±0.0005 -0.04 ±0.07 -0.52 0.11 17.24 1.18 23.04 405 70.651 -122.945 Surface 28.70 ±0.0004 -3.05 ±0.07 3.91 0.572 ±0.003 0.12 0.03 0.56 2.47 25 29.25 ±0.0002 -3.19 ±0.07 0.48 0.09 0.10 0.63 4.56 50 32.20 ±0.0002 -1.30 0.582 ±0.086 0.47 8.31 1.49 15.17 100 32.83 ±0.0003 -1.54 0.677 ±0.175 0.11 14.35 1.76 25.93 200 33.95 ±0.0003 -0.81 0.847 ±0.033 0.10 17.39 1.54 27.29 536 34.76 ± 0.0002 0.31 0.493 ±0.033 0.10 16.15 1.22 20.36 407 71.021 -126.087 Surface 27.02 4.73 0.936 ±0.080 0.00 0.28 0.36 2.81 25 29.69 1.38 0.15 0.89 0.60 3.85 50 31.94 -1.15 0.585 ±0.010 0.35 7.36 1.15 12.85 100 32.77 -1.52 0.375 ±0.002 0.01 13.34 1.53 24.60 200 33.34 -1.17 0.546 ±0.010 0.03 15.74 1.39 26.53 400 0.36 0.533 ±0.136 0.04 13.72 0.73 9.99 408 71.264 -127.497 Surface 27.59 ±0.0001 -3.22 ±0.07 1.82 0.08 0.02 0.64 2.63 25 29.25 ±0.0005 -2.86 ±0.07 1.43 0.761 ±0.151 0.08 0.03 0.76 2.72 50 29.33 ±0.0004 -2.85 ±0.07 -1.01 0.437 ±0.010 0.26 0.71 0.91 4.95 100 32.73 ±0.0008 -1.49 0.679 ±0.036 0.11 14.08 1.74 26.73 200 34.05 ±0.0007 -0.35 ±0.07 -0.78 0.773 ±0.235 0.09 16.82 1.55 27.28 420 71.053 -128.514 Surface 30.97 -0.66 0.472 ±0.055 0.32 1.89 0.86 7.07 25 31.51 -1.09 0.664 ±0.050 0.32 1.19 0.87 5.25 50 0.516 ±0.025 100 200 421 71.479 -133.948 Surface 22.44±0.0003 -5.86±0.04 1.82 0.12 0.02 0.32 8.52 25 30.27 ±0.0005 -2.84 ±0.04 -1.06 0.13 0.01 0.65 2.20 50 30.83 ±0.0004 -2.77 ±0.04 -1.44 0.15 4.53 1.06 9.45 100 32.51 ±0.0005 -1.42 0.14 12.58 1.62 24.52 200 33.63 ±0.0006 -0.89 ±0.04 -1.34 0.14 15.51 1.60 27.30 424 71.171 -133.831 Surface 22.92±0.0002 -5.81 ±0.04 1.05 0.16 0.04 0.25 11.06 25 30.12 ±0.0001 -1.27 0.16 0.04 0.62 2.35 50 30.78 -1.28 0.29 0.98 0.77 4.29 100 32.60 -1.46 0.12 12.82 1.60 25.25 200 34^09 -088 0.12 13.99 1.18 17.96 435 71.076 -133.666 Surface 28.37 ±0.0004 -0.58 ±0.04 1.82 0.737 ±0.079 0.03 0.03 0.60 3.48 25 29.87 ±0.0008 -2.65 ±0.04 -1.13 0.04 0.02 0.70 2.93 50 31.16 ±0.0011 -2.69 ±0.04 -1.34 0.491 ±0.076 0.20 3.69 1.05 9.47 100 32.76±0.0005 -1.45 0.462±0.023 0.04 14.19 1.72 28.99 200 34.72 ±0.0009 0.42 ±0.04 0.33 0.528 ±0.043 0.05 13.99 1.17 11.74 257 34.81 ±0.0007 0.55 0.828 ±0.026 0.04 13.68 0.93 9.26 434 70.177 -133.557 Surface 30.45 ±0.0007 -2.82 ±0.04 -1.61 0.31 4.13 1.43 17.80 25 31.01 ±0.0010 -3.17 ±0.04 -1.49 0.31 3.94 1.24 14.97 50 100 200 436 70.335 -126.353 Surface 29.49 ±0.0007 -3.01 ±0.04 1.06 0.502 ±0.007 0.09 0.01 0.64 3.23 25 31.57 ±0.0008 -2.44 ±0.04 -0.95 0.25 1.17 0.97 5.52 50 32.50 ±0.0002 -2.04 ±0.04 -1.52 0.673 ±0.080 0.26 10.77 1.60 19.46 100 32.98 ±0.0003 -1.53 0.739 ±0.159 0.10 14.47 2.14 28.13 200 34.45 ±0.0007 0.34 ±0.04 -0.24 0.451 ±0.018 0.07 15.71 1.40 23.75
85 subsequent deep water nutrient inputs are restricted to small upwelling events (40).
Across the estuary and shelf, nutrients are supplied primarily by the Mackenzie River and are then recycled throughout the water column. Easterly winds draw deeper waters to the shelf surface and force river plume waters offshore (6) and under favourable ice conditions the plume can be seen to extent to the shelf edge and 100 km into the interior ocean (41). Autotrophic and heterotrophic productions are in general highest across the estuary and shelf in late spring when irradiance and nutrient inputs from the river are maximal (42). Over the summer, as river discharge decreases, productivity also diminishes as surface waters become depleted in nutrients and primary producers are forced deeper in the water column (40).
Latitudinal Transect 1
This latitudinal transect consisted of eight stations (421, 422, 424, 435, 426, 428, 430 and
434) and was characterized by a dramatic change in depth. From 1000 m at station 421 to
40 m at station 434, the most southerly station positioned just off the Mackenzie delta
(Figure 7 a-b). As a result, water masses along this transect were divided into two distinct layers; a cold and fresher surface layer (Arctic water) from 0 to about 200 m with temperatures ranging from -1.5 °C at the surface to +0.5 °C from 200 m and below. A salinity gradient is also observed with the freshest water at the surface (31 psu) and a sharp increase to 32.5 psu beginning at about 50-75 m. Atlantic water dominated from
250 m and below. Nutrient profiles are shown in Figure 7 (e-i). High resolution surface
(5-30 m) temperature and salinity profiles, respectively, are shown in Figures 7b and d.
Station 434, located near the mouth of Mackenzie, is characterized by a cold and saline
86 Figure 7. a) temperature, b) temperature in surface layer c) salinity, d) salinity in surface layer, e) nitrite, f) nitrate, g) phosphate, h) silicate and i) N:P ratio contour plots for the sampling transects 1. Water THg concentrations are superimposed onto each of the 9 contour maps for station 435 on the Mackenzie Shelf-Beaufort Sea region.
Temperature (°Q a) mg(ng/L) 0.3 04 0.5 0.6 0.7 0.8 0.9 1
Ttrn w.rN Offshore Mac. Delta £ucfraefa200m
b) Temperature (°C)
Mac. Delta Offshore Latitude
87 c) Salinity (psu) THg(ng/L) 0.3 04 05 0.6 0.7 a8 0.9 1
32.S
!•„
KM 71.TH 71"N m.a°N me?N 70.^ Offshore Latitude Mac. Delta
Euc/raefa25m 777emfsto200m
d) Salinity (psu)
32.5
27.5
21.5
7WN mi 79.M Mac. Delta Offshore Latitude
88 e) NtriteftJV) THafaW 113 014 0.5 0.6 0.7 018 0.9 1
10.25 200H
0.2
JZ +J Q. |0.«5 a
lai
800-1
10.05
TWH HTM 7i°n nm n.m 79.4'N
0 Mtnate(jJVl)
"fHgWL) 03 0.4 0.5 06 07 0.8 09 1
12.5
n.m rim ft* mm MM m.4ti Longtude
89 g) Phosphate ftiVI)
T^(ngl) 03 04 05 06 07 08 09 1 il».75
<5
US
l».w
10.5
0.25 n.rN n.n* im mfN mrH TtA'H Longtude
h) Silicate (uM) THKrtfL) 03 04 as ae 0.7 as 09 1
130
i*>
nm 71W msnt Longtude
90 i) MP Ratio THKng/L) 03 04 as as a7 as a9 1
if 2.5
7.5
125
7U°N 71.FN 7fW T9.VN 7MTN 70.4'N
Longtucte
91 profile whereas the stations located offshore and aligned together off the Mackenzie have warm and fresh characteristics. This top 10 to 20 m of the water column is likely the result of the mixing of ice melt and runoff caused by storms throughout early autumn (6).
Nitrite (NO2") concentrations are lowest in the fresher Mackenzie River water. Higher concentration of nitrite in the deeper water can be attributed to, at least in part, the excretion of nitrite by phytoplankton during nitrate assimilation (43). High levels of nitrites (~ 0.3 uM) were observed at station 434. Interestingly, it has been shown that rivers flowing into the Arctic contribute a wide range of nutrients concentrations but waters below 50 m contain less than 10% river water (44). Nutrient depletion along the shelf may also be caused by convection due to ice formation (38). Phosphate and silicate
(Figures 7g and h), respectively, had a similar vertical profile across this transect. The nutrient rich Pacific-origin middle halocline waters between 50 and 300 m, results from the advection of nutrient-rich waters emanating from the Bering and Chukchi seas (44).
Finally, the N:P ratio (Figure 7i) ranged from almost 0 along the Mackenzie Shelf to 16 at the bottom of the water column at the deeper stations along the transect. Following a bloom, nutrients such as nitrate are depleted in waters above the pycnocline. The normal
N:P ratio value is 16:1 (Redfield ratio), which is constant between uptake and remineralisation when nutrients are not limiting. Since the main reservoir of nutrients is from the deeper waters, this could explain why the N:P ratio was very low in comparison to stations 421, 422, 424 and even 435.
92 Latitudinal Transect 2
This transect consisted of stations 410, 412, 414, 416, 418 and 420. The temperature plot shown in Figure 8a shows a warm surface layer, the upper Pacific halocline, between 0.5 and 1°C at station 410 and 412 which then cools to 0 °C at the most southerly stations 418 and 420. A band of colder water (-1.0 °C) between 50 and 200 m was observed along the entire transect. A strong salinity gradient was observed along this transect with concentrations ranging from -29.5 psu at the surface to 34 psu in the deep Atlantic water layer. Normally, Pacific water layer lies between 50 and 200 m but, this is generally subject to temporal variability (38). Shimada et al. (45, 46) and Steele et al. (47) reported the presence of two types of summer Pacific haloclines. In our study, the highest nitrate concentrations were observed in the upper halocline water, especially at station 418 and
420 with levels around 0.3 \imlh. The nitrate plot (Figure 8 d) shows low surface levels and a progressive increase with depth. Phosphate and silicate have high concentrations in the middle halocline water with values around or above 25 um/L for the silicates. N:P ratio was low at surface, with values near zero and reaches its normal 16:1 Redfield ratio value with increasing depth (Figure. 8 c-g). The general nutrient exhaustion observed in the surface layer under the form of a horizontal gradient indicates phytoplankton production and consumption (48). Stratification in the water upper layer, due to melting and/or formation of sea ice, severely limits the replenishment of nutrients to surface waters (91).
93 Figure 8. a) temperature, b) salinity, c) nitrite, d) nitrate, e) phosphate, f) silicate and g) N:P ratio contour plots for the sampling transect 2. Water THg concentrations are superimposed onto each of the 7 contour maps for station 420 on the Mackenzie Shelf- Beaufort Sea region. a) Temperature (°C) Hg(ng/L)
100
2001 I mi w 7ir* n.rw 7t.*m n.m rim n.i'H 71tt Latitude Euchaeta 5 m
Euchaeta 200 m
Salinity (psu) b) Hg(ng/L) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
i»
130
ri.ru n.m tt.ni Ti.ru nrn ?f.!** Latitude
94 c) Nitrite (MM) Hg(ng/L) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.25
0.15
Latitude
Nitrate (uM) d) Hg(ng/L) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
95 e) Phosphate (pM)
Hg(ng/L) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
mtt Latitude
f) Silicate (MM)
Hg(ng/L) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
a
96 g) Ratio MP Hg(ngl) 0.3 04 0.5 06 0.7 0.8 09 1
11.S
97 Longitudinal Transect 3
This longitudinal transect crosses through Amundsen Gulf consisted of five stations (420,
408, 407, 405 and 403). Water depths ranged from 40 m at station 420, the most south
westerly site, to 600 m at station 405. A warm and fresher surface water layer sat on top
of a cold and denser band located between 100 and 200 m (Figure 9a-b). Below the
Pacific middle halocline layer lies Atlantic origin water with temperatures and salinity
above 0 °C and 34 psu, respectively (Fig. 9 a-b). Interestingly, the deep water at station
407 had low nitrite (~0 uM), phosphate (~0.75 uM) and silicate (~15 uM) concentrations
and a remarkably high N:P ratio compared to the other stations on that same transect (Fig.
9 c-g). This suggests high silicate and phosphate uptake relative to nitrate (50). Depletion
of silicate relative to nitrate (NO3) suggests that the main consumers in this region are
silicate requiring groups such as diatoms (51). In estuarine and coastal regions,
characterized by seasonally varying mixtures of fresh and seawater, there is evidence for
seasonal and spatial variations in the limiting nutrients. As was observed in Transect 2
above, nutrient exhaustion observed in the surface layer under the form of a horizontal
gradient indicates phytoplankton production and consumption (48).
Franklin Bay (Station 436)
Station 436 is located near of Franklin Bay which is influenced by the Horton River and
steep bathymetry. This is an area characterised by frequent upwelling events and is an
important feeding area for mammals and fishes. Percent MMHg at this station was the
highest in Euchaeta (60.12 %) and among the highest in Calanus (61.83 %). Wells et al.
98 Figure 9. a) temperature, b) salinity, c) nitrite, d) nitrate, e) phosphate, f) silicate and g) N:P ratio contour plots for the sampling transect 3. Water THg concentrations are superimposed onto each of the 7 contour maps for station 420, 407, 405 and 403 on the Mackenzie Shelf-Beaufort Sea region.
a) Temperature (°C) Hg(ngfL) Hg(ngfL) Hg(ng/L) Hg(ngl) 0.3 0.4 0.5 0.0 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 19, 1 °-3 <" £•* 0.6 0.7 0.8 0.9 1
ml
2«H
•K 3001 © Q 400 m
mA
m-w fimr WW tWN tievr Longitude Euchaeta 5 m Euchaeta 200 m
Salinity (psu) b) Hg(ng/L) Hg(ng/L) Hg(ngrt-) Hg(ngl) 0.3 04 0.5 0.6 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 09 1 03 04 0.5 06 07 M 09 1
IM°W m°w fWW orw m°W Longitude Euchaeta 25 m
Themisto200m
99 c) NtriteftJVI) Hg(ngl) Hg(ngl-) Hg(n^L) Hg(n^L) a3 tt40. 5 0.6 a7 0.8 tt9 1 tt3 0.4 0.5 0.6 0.7 a8 ft9 1 0.3 04 05 06 0.7 0.8 0.9 1 0.3 04 05 06 0.7 05 0.9 1
12TW
d) NtrateftlM)
Hg(n^L) Hg(n^L) Hg(ngl-) KJWL) 0. 04 05 06 0. 0 0.9 1 0.3 0.4 0.5 0. 0.7 0.8 03 1 03 04 05 0.6 0.7 03 09 1 03 04 05 06 0. 0.8 0 1
100 e) Phosphate(l-M)
Hg(ngl) Hg(ngrt.) Hg(ngL) Hg(ngO-) 0.3 04 0.5 0.6 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 03 04 15 1X6 0.7 0.8 0.9 1 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
1WW
f) Silicate((iVl)
Hg(nc^L) Hg(ngl.) Hg^L) Hg(rtfL) 0.3 0.4 0.5 0.6 a7 0.8 0.9 1 0.3 04 0.5 0.6 17 0.8 05 1 0.3 0.4 0.5 0.6 0.7 0.8 09 1 0.3 O/t 0.5 0.6 0.7 0.8 0.9 1
101 301
V 6T>ffO IT) 9T> SO P0 CO I 60ffO iT > 9T> ST) m SO k 60 80 TO 9D ST) VO CD I 6T> CO IX) SO ST) Ml CO (-1A06H (TAi)en (lAi)6H (T/6U)6H
d:NO!iey (§ (22) looked at the particulate and microbial variables at several stations on the Mackenzie shelf and at two stations located in Franklin Bay including one positioned near 436 (52).
Generally, they found that their station located near the mouth of the Horton River in
Franklin Bay was under the influence of brackish waters with high surface concentration of bacterioplankton and Chlorophyll-a, compared to stations more influenced by marine waters. They also found that Franklin Bay had particle-rich waters and the Horton River was likely a particle source (52). The top ten meters at station 436 was characterised by a salinity of around 29.3 psu and a water temperature of about 1.05 °C and the bottom depth was 243 meters.
THg water concentrations and profiles
Six stations were sampled for THg in water including 405, 407, 408 and 420 in the
Amundsen Gulf, 436 in Franklin Bay and 435 in the Beaufort Sea. THg concentrations in water ranged from 0.38 to 0.94 ngL"1. The extreme values were both measured at station
407 in the Amundsen Gulf (Table 3). Unfortunately, due to the limited THg water data, it was difficult to determine any strong relationships with the water mass characteristics of the Mackenzie Shelf-Beaufort Sea area. Only one station was sampled along each of latitudinal transects 1 and 2. Along the first transect, at station 435, the highest THg concentrations were measured in the surface water (0.74 ± 0.11 ng/L) and in the Atlantic water layer (0.83 ng/L). At station 420 three water column measurements were made.
The highest HgT level was observed at 25 m just at the limit between Arctic waters in the surface and the upper halocline. Transect 3 consisted of four THg vertical profiles. No real trend was observed, however, the highest THg concentration measured at station 407
103 seemed to be associated with the fresher surface water (High T°C, low S). Finally,
Franklin Bay station 436 had the lowest THg concentration in surface and at 200 m.
PCA (see Methods section) was conducted to examine pattern similarities and differences between temperature, THg, salinity and nitrite concentrations with station number and
depth. The resulting score and loading plots are shown in Figure 10. The first and second
principal components (or factors) accounted for 44 and 26%, respectively, of the total
variability in the data set. Temperature and THg were strongly positively correlated with
surface waters, and negatively correlated with salinity and nitrite concentrations. These
results suggest that the higher THg concentrations were associated with the delivery of
Hg via the Mackenzie River. Leitch et al. (2008) reported that ~ 2000 kg of Hg are
delivered to the Beaufort Sea via the Mackenzie annually (9). Sea ice processes are also
known to be affecting Hg cycling, especially in shelf regions as sea-ice is an important
transport mechanism for Hg within and out of the Arctic Ocean, either by the
incorporation of shelf sediments through grounding or suspension freezing in shallow
continental seas or accumulation of atmospherically deposited Hg on ice (14,59).
Linkages between biological and physical processes
Figure 11 illustrates the salinity and 8180 values in the top surface layer (0-7.5 m) and
THg concentrations in the three zooplankton genus included in this study. The highest
THg levels were measure in the fresher water (depleted oxygen value and low salinity) at
104 Figure 10. Principal Component Analysis (PCA) results, a) Factor Loading Plot and b) Score Plot for data derived from the Mackenzie Shelf-Beaufort Sea region.
Factors Loading Plot Scores Plot
4l 1.0 I I I
J SAL
THG<\ 0.5-
* NITRITE
408-25m ?36-10Um 42125"212!m 405J50IT1 TH*^-^_^\ ana •iKfiAr 407-50m * 408-10ftf408-100^6.36.56o mi CM 40|-5m G. 0.0 - < j05-100m 420-5m 435-200m 435£0mk~ -1 43^100m J408-50m 4O7J00m
-0.5 -
-1.0 I 1 1 -1.0 -0.5 0.0 0.5 1.0 PCA1 (44%) PCA1
105 Figure 11. Spatial trends of a) salinity at surface, 2.5, 5.0 and 7.5 m, b) 8180 at surface, 2.5, 5.0 and 7.5 m and c) THg levels in Calanus spp., Euchaeta spp. and Themisto spp. on the Mackenzie Shelf-Beaufort Sea region.
106 stations 421, and 424. A strong negative correlation was observed between salinity (5 m) and THg in Calanus (^=0.72, p=0.009), Themisto (r^O.81, p=0.002) and Euchaeta
(^=0.94, p=0.000) (Table 4). In this section, THg, MMHg and %MMHg and measurements of stable isotope of carbon were used to explore relationships between these parameters and water masses properties at several depths and to develop linkages between water masses and zooplankton diet. While zooplankton vertical profile data were not yet available for the samples collected during the 2006 ArcticNet cruise, this study provides a description of the linkages found between water column features and zooplankton THg and MMHg concentrations, %MMHg and 813C (Table 3) in three main genus. Here, 813C was used as a predictor of where zooplankton may be feeding throughout the water column.
Darnis et al. (2007) looked at pre-winter zooplankton assemblages in south-eastern
Beaufort Sea in September and October 2002. They divided their area of study into three classes, the shelf, the slope and the polynya (52). They found that depth explained 71% of the variance in mesozooplankton composition among the stations and that salinity integrated from surface to bottom was closely correlated with depth and explained 68% of the variance. They report that mesozooplankton abundance and biomass were higher in the polynya than on the shelf or the slope. In the present study area, 421, 424 and 435 are located along the slope, 420, 408, 407, 405 and 403 in the polynya and finally, 434 and
436 over the shelf. They noted that the herbivorous copepods normally assemble in summer in the epipelagic layer (<200 m) and then move at deeper depth (200-1000 m) in the fall to form dense over-wintering aggregations. Their conclusions suggested that
107 depth, in association with the location of the Pacific halocline and Atlantic layer, was the most important variable explaining faunistic similarities. In general, the most diverse zooplankton assemblage was found when the three water masses were present and the largest biomass was in the polynya. The ice cover was reported to be the second most important factor in shaping pre-winter biogeography of the zooplankton.
Calanus spp
In this study, Calanus spp. consisted mainly of the larger adult older staged Calanus hyperboreus. THg in Calanus spp. was not only strongly correlated to salinity and 8180 but also to percent Pacific water and fraction of meteoric water and sea ice melt in surface waters. This result strongly suggests that Calanus spend time, probably during the late summer period, in the surface waters where they can acquire significant levels of inorganic Hg through passive absorption. The high Hg concentrations found in individuals collected on the shelf may be due to input of Hg (II) emanating from the
Mackenzie River (9) but could also be linked to other factors. Higher THg levels were found to occur in fresher water (low salinity and depleted oxygen) at warmer temperatures and to contain a smaller percentage of Pacific water. Calanus THg concentrations were also higher in waters containing a larger fraction of meteoric and sea ice melt (Table 5). The strong correlations observed between THg and salinity, 5180, percent Pacific water, fraction of meteoric water and sea ice melt at 5-25 m and also between S13C and fraction of sea ice melt at that same depth range suggest that the
Calanus hyperboreus were most likely feeding on phytoplankton and ice algae in surface waters throughout the bloom season. The higher THg Calanus spp. concentration in the
108 shelf region (station 424) could be attributed to number of factors. Darnis et al. (52) reported that the lowest Calanus hyperboreus biomass was measured in the shelf area of
the Beaufort Sea. Regions or zones with lower algal and zooplankton biomass could
result in increased Hg bioaccumulation as fewer organisms are available relative to the
Hg present in the water. This assumes, however, that there was not an excess of Hg
available in the water column. Recently, Outridge et al. (14) reported that the THg bound
up in the overall biomass of the entire Arctic ocean was only -1% of that present in the
upper 200 m of the water column. The Mackenzie shelf is known to have ice scour that
occurs over about 20% of the shelf in depth between 15 to 45 m and this can perturb and
re-suspend bottom sediments in the water column. As bottom sediments are known to
contain relatively high levels of Hg, re-suspension could enhance the exposure of
zooplankton to Hg (56).
Themisto spp.
As was observed in Calanus spp., THg and MMHg in Themisto were strongly correlated
with water mass properties in the surface layer. THg at 5 m was negatively correlated
with salinity, 8180 and percent Pacific water both positively correlated with FMW and
FSIM. MMHg between 25-50 m was positively correlated with FMW and FSIM (Table
4). This suggests that Themisto is probably spending time in the top surface layer where it
could accumulate Hg through absorption and/or feeding. However, since no relationship
was observed between 513C and physical properties from the top layer of the water
column, it remains uncertain if Themisto was feeding at that depth range or not but
109 Table 4. Summary table of the significant interactions between THg, MMHg, %MMHg of THg and 8I3C in Calanus, Euchaeta and Themisto with salinity, 5180, temperature, percent Pacific water, fraction of meteoric water (FMW) and fraction of sea ice melt (FSIM) Dep. Var. is the dependant variable, r2 is the correlation coefficient and p is the level of significance of the test on the Mackenzie Shelf-Beaufort Sea region. ,18, Genus Dep. Var. Depth (m)* Salinity (psu) SO (%o) Temp. (°C) % Pacific* FMW* FSIM*
2 2 2 2 r P r P r2 P r P r P P Calanus THg 5 0.72 0.009 0.75 0.005 0.56 0.032 0.68 0.012 0.60 0.025 MMHg 200 0.67 0.024 %MMHg 25 0.98 0.000 %MMHg 200 0.78 0.009 613C 25 0.55 0.050 Euchaeta THg 5 0.94 0.000 0.57 0.030 THg 50 0.88 0.002 0.76 0.050 MMHg 100 0.61 0.010 %MMHg 25 0.64 0.050 %MMHg 50 0.89 0.016 0.79 0.044 513C 5 0.49 0.65 0.029 25 0.66 0.050 0.65 0.050 0.81 0.006 200 0.57 Themisto THg 5 0.81 0.002 0.81 0.002 0.59 0.026 0.79 0.003 0.55 0.036 THg 100 0.92 0.001 MMHg 25 0.70 0.050 MMHg 50 0.70 0.050 MMHg 100 0.84 0.015 %MMHg 100 0.76 0.010 %MMHg 200 0.78 0.050 200 0.96 0.004 0.96 0.004 0.95 0.004 *Depths sampled - Salinity (surface, 2.5, 5, 7.5, 10, 25, 50, 100, 150, 200 m); 8180 (surface, 2.5, 5, 7.5, 10, 25, 50, 200 m); temperature (5, 10, 25,50,100, 150, 200); %Pacific (5, 10, 25, 50, 100, 125, 150, 200 m). Mean parameter values were used when consecutive depths showed significant correlations; ** Calculation from Jean-Eric Tremblay based on the method used by Jones et al. (1998) (57); *** Fraction of meteoric water (FMW) and Fraction of sea ice melt water (FSIM) calculated by Robbie Macdonald (1995) (30).
110 Table 5. Summary table of fraction of meteoric water (FMW), fraction of sea-ice melt water (FSIM), fraction of salty Atlantic water (FPML) and percent Pacific water at surface, 25, 50 and 200 m at each of the 9 stations on the Mackenzie Shelf-Beaufort Sea region.
Sample depth Bottom depth % Station FMW FSIM FPML (m) (m) Pacific 403 Surface 408 0.19 -0.05 0.85 67 25 0.17 -0.09 0.92 81 50 0.15 -0.08 0.94 77 200 0.02 -0.01 0.98 4 405 Surface 583 0.19 -0.01 0.82 62 25 0.21 -0.10 0.89 64 50 - - - - 200 - - - - 407 Surface 391 - - - 37 25 - - - 57 50 - - - 75 200 - - - 41 408 Surface 187 0.19 0.02 0.79 73 25 0.18 -0.02 0.84 83 50 0.18 -0.02 0.84 99 200 0.04 -0.02 0.98 52 421 Surface 1196 0.34 0.03 0.64 33 25 0.19 -0.06 0.88 75 50 0.18 -0.08 0.89 83 200 0.08 -0.05 0.97 69 424 Surface 560 0.33 0.06 0.62 24 25 - - - - 50 - - - - 200 - - - - 435 Surface 310 0.19 0.00 0.81 69 25 0.17 -0.04 0.87 80 50 0.18 -0.09 0.91 93 200 0.00 0.01 0.99 29 434 Surface 46 0.19 -0.07 0.88 100 25 0.21 -0.09 0.89 100 50 - - - - 200 - - - - 436 Surface 254 0.19 -0.04 0.85 73 25 0.17 -0.08 0.92 100 50 0.15 -0.09 0.94 100 200 0.00 0.01 0.99 43
111 correlations between both THg and MMHg with the surface properties suggest time spent by Themisto between 5-25 m. These results concur with the findings reported by Auel et al. (2003) in the Greenland Sea (59) and in a study done in Frobisher Bay, South eastern
Baffin Island, which showed that Themisto libellula occupied the upper 30 m throughout the year, with a clear peak abundance by late August and early September (61,62).
Dalpadado et al. (2001) found that highest abundance of Themisto libellula was associated with the Polar Front in the Barents Sea with juveniles prevalent in the surface waters (<25 m) and adults at depths between 100 and 200 m (63). In the present study, we can suggest from Dalpadado et al. observations in the Eastern Arctic that juveniles of the Themisto genus may also have been more common in surface waters.
THg, MMHg and %MMHg were also strongly correlated with water temperature at 100 m (Table 4). This depth is often corresponding to changes between arctic waters prevalent in surface and the presence and transition of the upper pacific halocline. THg and MMHg were positively correlated with increase in water temperature whereas
%MMHg was negatively correlated (Table 4). Finally, 813C was strongly correlated with water masses at 200 m (salinity, 5lsO and FMW) as such Themisto spp. was possibly moving vertically in the water column, likely getting inorganic Hg near the surface, especially at stations off the Mackenzie river, but probably feeding at greater depth as indicated by 5 C. From the salinity vertical profiles and 8 C relationships with 200 m of depth, it seems that Themisto is preferentially fed at the interface between the lower
Pacific halocline and the Atlantic water (Fig. 6b, 7b and 8b). Among the three genus studied, Themisto was found to have the most enriched average carbon signal (-25.5%o)
112 followed by Euchaeta (-27.8%o) and Calanus spp. (-30.3%o). The same phenomenon was also observed in the Eastern Arctic. These results suggest that Themisto may have fed more in pelagic waters rather than in the coastal ones.
Euchaeta spp.
In the carnivorous copepod Euchaeta spp. THg and 813C were both found to be strongly correlated with surface layer water properties (5-50 m) (Table 4). As indicated by 813C,
Euchaeta was possibly feeding in that range of depth (5-50 m). MMHg and 813C were also correlated with water mass properties between 100-200 m. The results suggest that
Euchaeta spp. may be feeding either primarily in the upper water column and accumulating Hg through both their diet and also through passive absorption in surface waters but also in deeper water. From the temperature vertical profiles and 813C relationships with 5 m and 200 m of depth, Euchaeta seems to be feeding at temperature above -1°C or the warmer zone above and below the cold layer of the Pacific halocline
(e.g. Fig. 7a). These results are in agreement with the findings described in both Longurst et al. (1984) and in Kaartvedt et al. (2002) that depicted Euchaeta has an interzonal diel migrant where both near surface and deep concentrations occurred together (64,65). Both studies found Euchaeta to have a bi-model vertical distribution with a predominant upper mode in summer time along with a more common deep mode through fall and early winter. They also described feeding to occur toward the surface especially for the smaller size individuals while the larger females were observed to be foraging successfully in deep water. Results from Vestheim et al. (2004) suggested that ovigerous females and individuals with great energy reserves to a large extent prioritize predator avoidance in
113 deep water versus feeding in the upper part of the water column (66). Numerous factors including food availability, predator avoidance, vertical water column stratification and light have been recognized to influence diel vertical migration (DVM) (66). Euchaeta has been described as a cruising raptor feeding on a variety of smaller zooplankton which include Calanus and cod larvae which would in turn explain its relatively mean value of enriched carbon signal found throughout the study area (67).
Generally, the relationships found between Hg and 813C with the water mass properties in all three genus showed that higher THg concentrations were associated with fresher water
(low salinity and warmer temperature) and with large fractions of both meteoric and sea- ice melt water. This strongly suggests that in the western Arctic, Hg uptake in zooplankton is highly driven by freshwater inputs into the system. In late summer early fall, organic matter resulting from the summer algal bloom are sinking toward the thermocline and into deeper waters. This is a critical period of time for the zooplankton as they are starting their descent into deeper waters for winter feeding and diapause.
In the current study we used the measured water columns characteristics and 813C and Hg in the zooplankton as tracers for their seasonal vertical distribution in the water column and feeding behaviour. In Calanus spp. strong correlations were observed between THg and all surface (<5 m) water characteristic with the exception of temperature. In addition, no correlation with 813C was observed suggesting that these animals were not feeding at this depth and that they were potentially acquiring Hg (II) via absorption. MMHg and
%MMHg were positively correlated with % Pacific water at 200 m but again, not with
114 8 C. While MMHg was not measured in the water column, Kirk et al. (2006) reported that higher MMHg concentrations generally occur in the deeper waters Calanus spp. is a specialized seasonal migrant who spend winter months in deep water (<1000 m). They start their ascent in early spring and spend summer months near surface water to feed actively and build up their lipids reserve and commence their descent usually in
September (68,69). But, the start time of ascent and descent in the water column depend on the area of the Arctic, the sex and of the maturity of the stage (70). Herbivorous copepods have been observed to be feeding in the sun-lit surface layer of high latitude ecosystems where high primary production and heavy grazing enable growth (Legendre et al., 1993), lipid-accumulation and, eventually, survival during the dark season (71).
Herbivorous copepods have been observed to be feeding in the sun-lit surface layer of high latitude ecosystems where high primary production and heavy grazing enable growth, lipid-accumulation and, eventually, survival during the dark season (72).
Among the three genus Euchaeta clearly showed a bi-modal vertical feeding mode.
Correlations between THg, %MMHg and S13C between 5-50 m strongly suggested that
Euchaeta were feeding within that depth range. MMHg therefore could be acquired through its diet and inorganic Hg by absorption via absorption nearer to the surface. 813C was correlated with temperature at 200 m but not with Hg. These results are in agreement with Kaartvedt et al. (2002) and Vestheim et al. (2005) that found Euchaeta to be an interzonal diel migrant where both near surface and deep concentrations occurred together (64,72). Finally, Themisto, like the Euchaeta, seem to acquire Hg (II) from the surface waters. S13C and %MMHg were correlated with salinity and 8180 at 200 m
115 suggesting Themisto to feed at that depth as was observed in Dalpadado et al. (2001) where adults of Themisto were feeding between 100-200 m in the Barents Sea in late summer (63).
Biomagnification Factors
Calculated biomagnifications factors (BMFs) for MMHg between Calanus spp. and
Themisto and Euchaeta spp. at each sampling locations in the Mackenzie-Beaufort Shelf area are shown in Figure 12. Values ranged between 1.99 to 4.70 for Themisto/Calanus and between 1.60 and 6.39 for Euchaeta/Calanus. The highest BMF values for both
Themisto/Calanus and Euchaeta/Calanus were observed at station 435 in Franklin Bay followed by station 403. MMHg BMFs for Themisto/Calanus at stations 421 and 424 could not be calculated due to the limited samples sizes. However, THg BMFs values were calculated to be 7.24 and 2.16 at each of these stations respectively.
For comparison, Table 6 lists MMHg BMFs from other regions across the Canadian
Arctic. Atwell et al. (66) reported BMF < 1 for zooplankton in Lancaster Sound. MMHg
BMFs between Calanus and Themisto spp. collected in 1997 from the NOW Polynya was calculated to be 9.40 using the values reported by Campbell et al. (34). Pazerniuk et al.
(73) reported MMHg BMF values from several regions within Hudson Bay System.
Themisto/Calanus values ranged between 1.26 (Eastern Hudson Bay) and 13.5 (Southern
Hudson Strait) and between 2.65 (Eastern Hudson Bay) and 17.6 (Foxe Channel) in
Euchaeta/Calanus.
116 Figure 12. MMHg Biomagnification factors (BMF) for the Mackenzie Shelf-Beaufort Sea region. Dark grey bars represent BMF between Themisto spp. and Calanus spp. and light grey bars represent BMF between Euchaeta spp. and Calanus spp.
S Themisto/Calanus Euchaeta/Calanus
403 405 408 421 424 435 436 Western Arctic locations
117 Table 6. Methyl mercury (MMHg) biomagnification factors (BMFs) in different areas of the Canadian Arctic.
Arctic region BMF Reference Mackenzie - Beaufort Shelf 1.99- 4.70 This study (2008)
North Water Polynya 2.75- 5.64 This study (2008) North Water Polynya 9.40 Campbell et al. (2005)
Lancaster Sound < 1* Atwelletal. (1998) Arctic Archipelago 2.98 This study (2008)
Eastern Hudson Bay 1.26 Pazerniuk et al. (2007) Southern Hudson Strait 13.5 Pazerniuk et al. (2007)
* BMF reported in Atwell et al. study was calculated with THg.
118 Implication for marine mammals
The Arctic is currently experiencing dramatic changes due to a warming climate (76).
Consequently, marine mammals that live in the Arctic may see their seasonal distributions, geographic ranges, patterns of migration, abundance, nutritional and reproductive success transform in several ways depending on their ability to adapt to these changes in their environment (e.g. disappearance of the ice cover). The potential impacts of climate change on marine mammals have been recently described in
Learmonth et al. (2006) who divided them into two categories, the direct and the indirect impacts (77). Direct impacts included effects linked to changes in sea level, sea ice cover and sea temperature. Changes in prey availability and accessibility are an example of indirect effect that could lead to an increase in susceptibility of the animals to disease and contaminants (77). Recent findings suggest that climate warming will also result in increased bioavailability of MeHg (8,9,14,78) and thus potentially higher exposure to aquatic biota. In this study, zooplankton had higher levels of THg and MMHg at stations located offshore from the Mackenzie River (Fig. 2 d-i). Marine mammals, fishes and birds feeding on the shelf and on the slope could therefore be exposed to higher levels of
Hg.
The Canadian Shelf in the Beaufort Sea supplies habitat for an active biological community of residents such as fish, seals and polar bears and to migratory populations including bowhead and beluga whales and a range of bird species (74). The diversity of animals in this region however, is significantly lower compared to other areas of the
Arctic such as Baffin Bay (74). The western Arctic marine and coastal region is
119 characterized by extreme conditions including ice cover, strong winds and large temperature range. Thus, living and transiting animals must be well adapted in order to forage and exploit this area (6).
One of the species that inhabits the eastern Beaufort Sea is the beluga whale
(Delphinapterus leucas). They congregate in the Mackenzie estuary in early summer. In
August, they move eastward into the Amundsen Gulf and Viscount Melville Sound and migrate westward along the Alaskan coast and far offshore (79). Annually, Inuvialuit from several communities harvest beluga whales and consume the animal as part of their traditional diet. Beaufort beluga whales have some of the highest Hg levels among
Canadian beluga whale populations as their liver Hg levels in this beluga population tripled in the 1990's in comparison to 1980 levels (12,15). Loseto et al. (2008) described habitat selection and Hg levels in the Beaufort Sea beluga whale population by looking at their diet. They found that beluga length drives diet variability which, in turn, led to differences in Hg uptake and food web biomagnification (80). Habitat selection related to length but also depended on sex and the reproductive status of the whale. In the western
Arctic, smaller males and females with calves seem to prefer open water habitat near the mainland and larger males closed ice cover near and in the Archipelago (81). Recently,
Stern and Macdonald (2005) showed that there was an approximate 2-fold decrease in concentration of THg and MMHg in Calanus hyperboreus from the Canada Basin to the
Chukchi Sea and Mendeleev Abyssal Plain (8). The origin of increasing Hg concentrations in western stocks of beluga whales could be linked to the foraging regions along prey concentration and fronts.
120 The Bowhead whale (Balaena mysticetus) is also a seasonal migrant in the Canadian
Western Arctic as it occupies the open-water area of the south eastern Beaufort Sea and the Amundsen Gulf as part of its summer range. Although limited satellite-linked telemetry data are currently available (73), Bradstreet and Fissel (1987) reported bowhead whales feeding on dense aggregations of mysids (Mysis oculatd) near the interface of the Mackenzie River with the saline waters of the offshore Beaufort Sea
(83,84). Generally, contaminant levels in bowhead whales are significantly lower than the ones observed in odontocete cetaceans such as the beluga whale. Bowhead whale is a mysticete that filtrates large amount of water with their baleen and feed at lower trophic levels by preying on zooplankton (17,85). However, bowhead exposure to Hg could change along with the warming climate and habitat availability (80).
Other species of marine mammals including the ringed seal and the much larger bearded seal are living in the southeastern Beaufort Sea and Amundsen Gulf. Ringed seal (Phoca hispidus) can not be classified as resident or transient specie within the study area. Even though ringed seals are present year-round in the coastal waters of the Beaufort Sea-
Amundsen Gulf area, they are very mobile and their movements may confound the interpretation of population surveys and contaminants data. Tagging and tracking work done on ringed seals in the Western Arctic using satellite telemetry have shown that some animals travelled up to 2625 km (75). Levels of contamination of Hg in higher trophic level mammals such as seals which feed on zooplankton and fishes may reflect very high levels of Hg in top predator such as the polar bear. Wagemann et al. (86) showed that the ringed seal population from the Western Arctic had significantly higher concentration of
121 Hg than the one from the Eastern Arctic. They also found the same pattern in the beluga whales with higher Hg levels in the Western Arctic. Most recently, Outridge et ah (2002) showed that Hg levels have increased in Canadian Arctic marine mammals from pre- industrial times to the present (86), but temporal trend data sets for Hg in beluga, ringed seals, moose, seabirds and fish based on the past 20-30 years show conflicting trends especially in beluga and ringed seals that show significant year to year variability combined with a high variance within years (87).
The diversity of marine birds in the south eastern Beaufort Sea is also much lower than in the Eastern Arctic or in the Chukchi Sea areas. Brant (Branta bernicla) and King Eider
(Somateria spectabilis) are the only marine bird species harvested in substantial numbers in this area of study (88). Highest abundance of King Eider normally occurred west of the
Mackenzie River mouth toward Cape Bathurst and along the south western side of Banks
Island. King Eider forages on sea bed benthic species and therefore is more vulnerable to
Hg accumulation than Brant that is a grazer specie (89).
Generally, marine mammals are moving actively within or through the Beaufort Sea-
Amundsen Gulf area either as a resident or a visitor. In both cases, animals feeding off the Mackenzie river on the slope and on the shelf are subject to higher Hg levels assimilation according to the levels measured in zooplankton which is the main food sources sustaining the higher trophic levels. Seals and beluga whales are subject to higher levels of MMHg than fish or bowhead whales as they feed at higher trophic level positions. Biomagnification factors between Themisto/Calanus and Euchaeta/Calanus
122 were higher at station 435 which is on the slope off the shelf. It is difficult to predict
BMF at higher trophic levels since it may vary along several factors including species, age and sex, water masses changes, feeding patterns etc. Thus, results from this study suggest that marine mammals and fishes feeding near or at station 421, 424 and 435 are potentially susceptible to assimilate more Hg than animals feeding in Franklin Bay or in the Amundsen Gulf.
123 References
(1) O'Brien, M.C.; Macdonald, R.W.; Melling, H.; Iseki, K. Continental Shelf Research 2006, 26, 41-81. (2) Macdonald, R.W.; Harner, T.; Fyfe, J.; Loeng, H.; Weingartner, T. Arctic Monitoring and Assessment Programme (AMAP), Oslo, Norway. 2003, xii+65 pp. (3) Macdonald, R.W.; Harner, T.; Fyfe, J. Science of the Total Environment 2005, 332, 5-86. (4) Hop, H.; Pearson, T.; Hegseth, E.N.; Kovacs, K.M.; Wiencke, C; Kwasniewski, S.; Eiane, K. Polar Research 2002, 21,167-268. (5) Carmack, E.C.; Macdonald, R.W.; Papadakis, J.E. Journal of Geophysical Research 1989, 94, 18043-18055. (6) Carmack, E.C.; Macdonald, R.W. Arctic 2002, 55, 29-45. (7) Dunton, K.H.; Weingartner, T.; Carmack, E.C. Progress in Oceanography 2006, 71, 362-378. (8) Stern, G.A.; Macdonald, R.W. Environmental Science & Technology 2005, 39, 4707-4713. (9) Leitch, D.R.; Carrie, J.; Lean, D.; Macdonald, R.W.; Stern, G.A.; Wang, F. Science of the Total Environment 2006, xx, xxx-xxx. (10) Morel, F.M.M., Kraepiel, A.M.L., Amyot, M. Annu. Rev. Ecol. Syst. 1998, 29, 543-566. (11) Barkay, T.; Poulain, A.J. Federation of European Microbiological Societies 2007, 59,232-241. (12) Loseto, L.L., Stern, G.A., Deibel, D., Connelly, T.L., Prokopowicz, A. Lean, D.R.S., Fortier, L., Ferguson, S.H. Journal of Marine Systems 2007, (In Press). (13) Schroeder, W.H., Anlauf, K.G., Barrie, L.A., Lu, J.Y., Steffen, A., Schneeberger, D.R. Nature 1998, 394, 331-332.). (14) Kirk, J.L.; Louis, V.L.S.; Sharp, M.J. Environmental Science and Technology 2006, 40, 7590. doi:7510.1021/ES061299. (15) Outridge, P.M.; Macdonald, R.W.; Wang F.; Stern G.A.; Dastoor, A.P. Environmental Chemistry 2008, 5, 89-111. (16) Lockhart, W.L.; Stern, G.A.; Wagemann, R.; Hunt, R.V.; Metner, D.A.; DeLaronde, J.; Dunn, B.; Stewart, R.E.A.; Hyatt, C.K.; Harwood, L.; Mount, K. Science of the Total Environment 2005, 351-352, 391-412. (17) Hobson, K.A., Fisk, A., Karnovsky, N., Hoist, M., Gagnon, J.M., Fortier, M. Deep-Sea Research II2002, 5131 -5150. (18) Dehn, L.-A.; Follmann, E.H.; Thomas, D.L.; Sheffield, G.G.; Rosa, C; Duffy, L.K.; O'Hara, T. M. Science of the Total Environment 2006, 362,103-123. (19) Tamelander, T., Soreide, J.E., Haakjon, H., Carroll, M.L. Journal of experimental marine biology and ecology 2006, In Press. (20) Atwell, L., Hobson, K.A., Welch, H.E. Can. J. Fish. Aquat. Sci. 1998, 55, 1114- 1121. (21) Schell, D.M.; Barnett, B.A.; Vinette, K.A. Marine ecology progress series 1998, 7(52,11-23.
124 Dehn, L.-A.; Follmann, E. H.; Rosa, C; Duffy, L. K.; Thomas, D. L.; Bratton, G. R.; Taylor, R. J.; O'Hara, T. M. Marine Pollution Bulletin 2006, 52, 301-319. Dietz, R.; Riget, F.; Hobson, K.A.; Heide-Jorgensen, M.P.; Moller, P.; Cleemann, M.; Boer, J.D.; Glasius, M. Science of the Total Environment 2004, 331, 83-105. Saupe, S.M.; Schell, D.M.; Griffiths, W.B. Marine Biology 1989,103, 427-432. Schell, D.M.; Saupe, S.M.; Haubenstock, N. Marine Biology 1989,103, 433-443. Macdonald, R.W. The Freshwater Budget of the Arctic Ocean. 2000, Dordrecht, MA, 383-407. Macdonald, R.W.; Yunker, M.B.; Gobeil, C. In: R. Stein and R.W. Macdonald, Editors, The Organic Carbon Cycle in the Arctic Ocean, Springer. 2004, 177-193. Grasshoff, K. 1999, 600 pp. Bauch, D.; Erlenkeuser, H.; Andersen, N. Global and Planetary Change 2005, 48, 165-174. Macdonald, R.W.; Paton, D.W.; Carmack, E.C.; Omstedt, A. 1995,100, 895-919. Uthe, J.F.; Solomon, J.; Grift., N. Journal - Association of Official Analytical Chemists 1972, 55, 583-589. Cai, Y. International Journal of Environment and Analytical Chemistry 1997, 68, 331-345. Murry, B.A.F., John M.; Teece, Mark A.; Smyntek, P.M. Canadian Journal of Fisheries and Aquatic Sciences 2006, 63, 2167-2172. Campbell, L.M., Norstrom, R.J., Hobson, K., Muir, D.C.G., Backrus, S., Fisk, A.T. Science of the Total Environment 2005, 351-352, 247-263. Kainz, M.; Telmer, K.; Mazumder, A. Science of the Total Environment 2006, 365,271-282. Mintenbeck, K.; Brey, T.; Jacob, U.; Knust, R. Journal of Fish Biology 2008, 72, 815-830. McConnaughey, T.; McRoy, C.P. Marine Biology 1979, 53, 257-262. McLaughlin, F.A.; Carmack, E.C.; Macdonald, R.W.; Melling, H.; Swift, J. H.; Wheeler, P.A.; Sherr, B.F.; Sherr, E.B. Deep-Sea Research 12004, 51, 107-128. Macdonald, R.W.; Wong, C.S.; Erickson, P.E. Journal of Geophysical Research 1987,92, 2939-2952. Carmack, E.C., Macdonald, R.W., Jasper, S. Mar. Ecol. Prog. Ser. 2004, 277, 37- 50. Macdonald, R.W., Carmack, E.C., McLauglin, F.A., Iseki, K., Macdonald, D.M., O'Brian, M.O. Journal of Geophysical Research 1989,94,18057-18070. Parsons T.R.; Webb D.G.; Rokeby B.E.; Lawrence M.; Hopky G.E. Polar Biology 1989, 9, 261-266. Dore, J.E.; Karl, D.M. Limnology and Oceanography 1996, 41,1619-1628. Cooper, L.; Whitledge, T.; Grebmeier, J.; Weingartner, T. Journal of Geophysical Research 1997,102, 12563-12573. Shimada, K.; Carmack, E.C.; Hatakeyama, K.; Takizawa, T. Geophys. Res. Lett. 2001, 28, 3441-3444. Shimada, K.; McLaughlin, F.; Carmack, E.; Proshutinsky, A.; Nishino, S.; Itoh, M. Geophys. Res. Lett. 2004, 31, L20301, doi: 20310.21029/22004GL020860. Steele, M.; Morison, J.; Ermold, W.; Rigor, I.; Ortmeyer, M.; Shimada, K. J. Geophys. Res. 2004,109, C02027, doi: 02010.01029/02003JC002009.
125 Luchetta, A.; Lipizer, M.; Giorgio, S. Journal of Marine Systems 2000, 27, \11- 193. Hall, P.O.; Hulth, S.; Hulthe, G.; Landen, A.; Tengberg, A. Journal of Sea Research 1996, 35, 123-137. Reigstad, M.; Wassmann, P.; Riser, W.C.; Oygarden, S.; Francisco, R. Journal of Marine Systems 2002, 38, 9-29. Wells, L.E.; Cordray, M.; Bowerman, S.; Miller, L.A.; Vincent, W.; Deming, J. W. Limnology and Oceanography 2006, 51, 47-59. Darnis, G.; Barber, D. G.; Fortier, L. Journal of Marine Systems 2007, vVXj AAA" XXX. Yamamoto-Kawai, M.; Tanaka, N.; Pivovarov, S.; Timokhov, L. Joint Poster Session 1, Formal Poster Viewing - Polar Coastal Processes (Joint with Sixth Conference on Coastal Atmospheric and Oceanic Prediction and Processes and the 8th Confon Polar Meteorology and Oceanography). 2005. Pickhardt, P.C.; Folt, C.F.; Chen, C.Y.; Klaue, B.; Blum, J.D. Ecology 2002, 99, 4419-4423. Yunker, M.B.; Macdonald, R.W. Arctic 1995, 48,118-129. Compeau, G.C.; Bartha, R. Applied and Environmental Microbiology 1985, 50, 498-502. Hill, P.R.; Blasco, S.M.; Harper, J.R.; Fissel, D.B. Continental Shelf Research 1991,11, 821-842. Jones, E. P.; Anderson, L. G.; Swift, J. H. Geophysical Research Letters 1998, 25, 765-768. Nurnberg, D.; Wollenburg, I.; Dethlef, D.; Eicken, H.; Kassens, H.; Letzig, T.; Reimnitz, E.; Thiede, J. Marine Geology 1994, 119, 185. doi:110.1016/0025- 3227(1094)90181-90183. Auel, H.; Werner, I. Journal of experimental marine biology and ecology 2003, 296, 183-197. Percy, J. Polar Biology 1993,13, 131-139. Dalpado, P.; Borkner, N.; Bogstad, B.; Mehl, S. Journal of Marine Science 2001, 58, 876-895. Longhurst, A.; Sameoto, D.; Herman, A. Journal of Plankton Research 1984, 6, 137-168. Vestheim, H.; Kaartvedt, S.; Edvardsen, B. Journal of Plankton Research 2004, 27. Lagadeuc, Y.; Boute, M.; Dodson, J.J. Journal of Plankton Research 1997, 19, 1183-1204. Greene, C. H.; Landry, M.R. Ecology 1985, 66, 1408-1416. Conover, R. J.; Huntley, M. Journal of Marine Systems 1991, 2, 1-41. Ritcher, C. ICES J. mar. Sci. 1995, 52, 533-539. Hirche, H-J.; Hagen, W.; Mumm, N.; Richter, C. Polar Biology 1994, 14, 491- 503. Kattner, G.; Hagen, W.J. Mar. Sci. 1995, 52, 329-335. Kaartvedt, S.; Trine, D.; Espen, B.; Tom, V. Journal of Plankton Research 2002, 24, 155-158. (74) Pazerniuk, M.A. Master of Science Thesis - University of Manitoba 2007, 1-157.
126 (75) Stirling, I. Arctic 2002, 55, 59-76. (76) NWT Environmental Audit Status of the Environment Report - SENES Consultants Limited 2005, 4-50. (77) Hoye, T.T.; Post, E.; Meltofte, H.; Schmidt, N.M.; Forchhammer, M.C. Current Biology 2007,17, R449-R451. (78) Learmonth, J. A.; Macleod, C. D.; Santos, M. B.; Pierce, G. J.; Crick, H. Q. P.; Robinson, R. A. Oceanography and Marine Biology: An annual Review 2006, 44, 431-464. (79) Department of Fisheries and Oceans DFO Science Stock Status Report E5-38 2000,1-14. (80) Loseto, L.L.; Stern, G.A.; Ferguson, S.H. Environmental Science and Technology 2008, xxx, 000-000. (81) Loseto, L.L.; Richard, P.; Stern, G.A.; J.Orr; Ferguson, S.H. Canadian Journal of Zoology 2006, 84, 1743-1751. (82) Bradstreet, M.S.W.; Fissel, D.B. LGL Ltd. Bowhead whale food availability in the southern Beaufort Sea: 1985 and 1986. Environmental Studies No. 50. Ottawa: Indian and Northern Affairs Canada. 1986. (83) Bradstreet, M.S.W.; Fissel, D.B. Part 1. In: LGL Ltd. Bowhead whale food availability characteristics in the southern Beaufort Sea: 1985 and 1986. Environmental Studies No. 50. Ottawadndian and Northern Affairs Canada. 1987. (84) Hoekstra, P.F.; Dehn, L.A.; George, J.C.; Solomon, K.R.; Muir, D.C.G.; O'Hara, T.M. Can. J. Zool. 2002, 80, 223-231. (85) Wagemann, R.; Lockhart, W.L.; Welch, H.; Innes, S. Water, Air and Soil Pollution 1995, 80, 683-693. (86) Cartridge, P.M.; Hobson, K.A.; McNeely, R.; Dyke, A.. Arctic 2002, 55, 123-132. (87) Muir, D.C.G.; Shearer, R.G.; Oostdam, J.V.; Donaldson, S.G.; Furgal, C. Science of The Total Environment 2005, 351-352, 539-546. (88) Dickson, D.L.; Gilchrist, H.G. 2002, 55, 46-58. (89) Suydam, R. S. The Birds of North America 2000,491 A. Poole and F. Gill, eds. (90) Auel, FL; Harjes, M.; Da Rocha, R.; Stubing, D.; Hagen, W. Polar Biology 2002, 25, 374-383. (91) Luchetta, A.; Lipizier, M.; Socal, G. Journal of Marine Systems 2000, 27, 177- 193.
127 Chapter 4 - Conclusion
This study was designed to examine the linkages between mercury (Hg) and stable isotopes of carbon (813C) in three ubiquitous zooplankton genus and water masses in two key Canadian High Arctic regions: the North Water polynya in the Eastern Arctic and the
Mackenzie shelf - Amundsen Gulf region in the Western Arctic. The emphasis was placed on the herbivorous copepod Calanus spp., mostly adult Calanus hyperboreus, the
Carnivorous copepod Euchaeta spp. and the hyperiid amphipod Themisto spp., mostly
Themisto libellula. Water masses were defined using several measures of physical and chemical parameters including salinity, temperature, 5180, nutrients (e.g. nitrate, nitrite, phosphate, silicate, N:P). A summary of the findings for both regions is shown in Table 1 which provides a comparison between vertical distribution in the NOW Polynya and in the Western Arctic for Calanus spp, Euchaeta spp. and Themisto spp.
In the NOW Polynya, part of the assimilation of the mercury and carbon in lower trophic level species could be attributable to differing water masses. The maximum THg value in sea water (2.34 ± 0.43 ng/L) was observed at station 118 near the coast of Ellesmere
Island and reflected the correspondingly high concentrations of THg and MMHg measured in Calanus spp. (19.2 ±1.2 and 7.2 ng/g) and Euchaeta spp. (83.4 ± 23.7 and
50.0 ng/g) at that same station. Measurements of depleted SlsO signal, lower salinity and nitrate levels and high THg levels in the water column at Station 118 suggest that sub- glacial melt from the Prince of Wales ice cap (POW) could be a source of mercury to the
Smith Sound region of the NOW polynya, based on these results. Further studies will be
128 carried out in late summer 2008 as part of a newly funded ArcticNet Phase II project to test this hypothesis. The relationships observed between THg, MMHg, %MMHg and
513C in all there major zooplankton taxa and water mass properties suggested uptake of inorganic mercury through absorption near surface water (5-25 m for Calanus spp., 5-50 m for Euchaeta spp. and 25-50 m for Themisto spp.). Uptake of MMHg through diet occurred between 25-50 m and 200 m in Calanus and Themisto and at 5-50 m and 200 m in Euchaeta spp.
In the Western Arctic, higher THg concentration in sea water was associated with fresher water (low salinity and warmer temperature) and with large fractions of both meteoric and sea-ice melt water. This strongly suggests that in the western Arctic, inorganic Hg uptake in zooplankton via-absorption near surface water was driven by freshwater inputs into the system. The relationships observed between THg, MMHg, %MMHg and 513C in all there major zooplankton taxa and water mass properties suggested feeding and uptake of inorganic mercury through absorption near surface water (5-50 m for Themisto and
Euchaeta and 5-25 m for Calanus) and feeding and uptake of MMHg through diet near
200 m.
Stable isotopes of carbon and nitrogen and mercury concentrations (THg, MMHg, and
%MMHg) for several zooplankton genus in three main areas of the Canadian High Arctic are listed in Table 2. Calanus spp. had a depleted 813C in both the Western (-28.6%o) and the Eastern Arctic (-29.4%o) and a more enriched value in the Archipelago (-26.2%o).
815N in Calanus spp. was more enriched as we move westward (8.6%o in the Archipelago
129 and 10.4%o in the Western Arctic) compared to the Eastern Arctic (8.0%o). THg, MMHg and percent MMHg were the lowest in the Eastern Arctic (12.6 and 4.8 ng/g, 38.2%). All three variables were more elevated in the Archipelago (18.2 and 8.1 ng/g, 45.5%) while the highest concentrations of THg and MMHg were found in the Western Arctic (23.3 and 10.1 ng/g, 44.8%).
In Euchaeta spp., 8 C was more depleted and 815N was more enriched in the Western
Arctic (-26.9 and 13.1%o) compared to the Archipelago (-24.6 and 11.3%o) and the
Eastern Arctic (-25.2 and 11.4 %o). The lowest THg in Euchaeta spp. was measured in the Archipelago (47.5 ng/g) while THg concentrations were higher in the Eastern (75.6 ng/g) and in the Western (81.3 ng/g) portion of this area of study. MMHg and percent
MMHg were both greater in the Western Arctic (44.3 ng/g, 54.9%) compared to the
Eastern Arctic (39.0 ng/g, 52.5%) while no data for MMHg in Euchaeta spp. was available in the Archipelago.
In Themisto spp., 813C was less depleted in the Eastern Arctic (-21.5%o) compared to the
Archipelago (-25.3%o) and the Western Arctic (-25.8%o). The highest 815N was measured in the Western Arctic (11.7%o) followed by the Archipelago (10.5%o) and the Eastern
Arctic (9.8%o). Both the highest THg and MMHg concentrations were measured in the
Western Arctic (65.5 and 33.2 ng/g) together with the smallest percent MMHg (51.9%).
In the Archipelago, THg and MMHg in Themisto spp. were of 56.4 and 29.9 ng/g, respectively and percent MMHg was the highest among the three areas (57.6%). Finally,
130 THg and MMHg were the lowest in the Eastern Arctic (48.8 and 23.0 ng/g) and percent
MMHgwasof50.8%.
In summary, the general trend in the results illustrated in Table 2 showed that the average
8 C value in all genus was more depleted in the Western Arctic and this is due to the influence of the Mackenzie River. The average 815N value in all genus was more elevated in the Western Arctic which mean that the trophic level in this area of the Arctic among zooplankton is higher. Sagitta sp., Calanus sp., Euchaeta sp., Themisto sp., Limacina helicina and Hyperoche sp. had the highest THg in the Western Arctic. MMHg results in other genus than Calanus, Euchaeta and Themisto are more variable because we were only able to analyse individuals at a few stations because of time and sample sizes.
Future studies should be performed on each one of these genus, as their biology differ from one another, and should be done in relation to the physical and chemical features of the different areas throughout the Canadian Arctic.
As the Arctic environment is experiencing rapid and numerous environmental changes, the present study showed that zooplankton were highly dependent on water mass structure. Feeding, mercury uptake and both spatial and vertical distributions appeared to be related to specific physical and chemical properties of the water column. While our study was restricted to late summer (late August and September), results will vary seasonally depending on sea ice type and concentration, darkness and the onset of the spring bloom factors that affect zooplankton position in the water column. The current
131 IPY Circumpolar Flaw Lead (CFL) System study was designed in part to study these seasonal differences and with a wider range of taxa.
132 Table 1. Vertical distribution in the NOW Polynya and in the Western Arctic as suggested from the data in this study and what has been described in the literature in other areas of the Arctic for Calanus spp, Euchaeta spp. and Themisto spp.
NOW Polynya Vertical Distribution Western Arctic Vertical Distribution Vertical Distribution Genus (this study) (this study) (literature)
5-25 m (Feeding, uptake of MMHg; Hg (II) via 5-30 m (Dawson, 1978 - Summer in Central Arctic Ocean; Hermann, 1983 - Calanus spp. 5-25 m (Uptake of Hg (II) via absorption*) absorption*) August Baffin Bay; Longhurst et al. 1984 - Late summer Baffin Bay.)
25-50 m (Feeding, uptake of MMHg) <50 m (Astthorsson and Gislason, 2003 June and July in Iceland Sea). ~200 m (Dawson, 1978 - Fall in Central Arctic Ocean; Longhurst et al. 1984 - 150-200 m (Feeding, uptake of MMHg) 200 m (Feeding, uptake of MMHg) Late summer Baffin Bay). 5-50 m (Feeding, uptake of MMHg; Hg (II) via 5-50 m (Feeding, uptake of MMHg; Hg(ll) via Euchaeta spp. absorption*) absorption*) Bi-modal feeding (Kaarvedt et al. 2002 - Late summer Norwegian fjord; Vestheim et al. 2005 - Spring and fall Norway). 200 m (Feeding) 200 m (Feeding, uptake of MMHg) 25-50 m (Feeding, uptake of MMHg; Hg (II) via 5-50 m (Feeding, uptake of MMHg; Hg (II) via 5-30 m (Percy, 1993 - August and September in Frobisher Bay; Auel et al. Themisto spp. absorption*) absorption*) 2003 - August in Fram Strait). 100-200 m (Dalpadado et al. 2001 - September and October in Barents Sea 150-200 m (Feeding, uptake of MMHg) 200 m (Feeding, uptake of MMHg) (Adult)).
* As measured by 813C, THg, MMHg and %MMHg (see Table 2 in Chapter 2 and Table 1 in Chapter 3).
133 Table 2. Stable isotopes of carbon and nitrogen (813C and 515N), total mercury (THg), methyl mercury (MMHg) and percent methyl mercury in THg (%MMHg) in various genus from the Eastern Arctic, the Arctic Archipelago and the Western Arctic. Area Taxonomic Group - Genus n 513C(96o) SE 815N (%o) SE THgOgg1) SE MMHg (ng g"1) SE %MMHg Eastern Chaetognatha - Sagitta sp. 9 -23.5 0.3 10.2 1.4 17.6 0.3 9.3 0.4 52.8 Arctic Copepod Calanoid - Calanns sp. 9 -29.4 0.4 8.0 0.0 12.6 3.0 4.8 1.2 38.2 Copepod Calanoid - Euchaeta sp. 7 -25.2 0.4 11.4 0.1 75.6 2.9 39.0 11.0 52.5 Hyperiidea Amphipod - Themisto sp. 8 -21.5 0.4 9.8 0.1 48.8 9.0 23.0 3.4 50.8 Gammaridea Amphipod - Apherusa sp. 5 -23.4 0.9 7.7 0.2 21.1 2.8 Gammaridea Amphipod - Onisimus sp. 5 -17.8 0.5 8.3 0.2 27.1 2.8 Pteropod - Cliona limacina 6 -19.8 0.5 8.4 0.2 52.1 2.8 11.8 1.4 22.6 Pteropod - Limacina helicina 7 -21.7 0.5 8.5 0.3 32.3 1.5 9.3 0.9 28.8 Fish larvae - Boreogadus saida 6 -22.8 0.4 9.0 0.1 35.9 2.2 15.6 1.3 43.5 Euphausiacea - Thysanoessa sp. 1 -20.7 0.4 9.6 0.1 22.4 .2.2 Arctic Chaetognatha - Sagitta sp. 12 -23.0 0.2 10.9 0.2 20.7 0.4 10.3 0.6 50.0 Archipelago Copepod Calanoid - Calamus sp. 10 -26.2 0.2 8.6 0.2 18.2 0.8 8.1 0.1 45.5 Copepod Calanoid - Euchaeta sp. 8 -24.6 0.4 11.3 0.2 47.5 1.8 Hyperiidea Amphipod - Themisto sp. 9 -25.3 0.4 10.5 0.2 56.4 1.1 29.9 0.7 57.6 Gammaridea Amphipod - Gammarns sp. 5 -17.6 0.6 8.5 0.4 43.8 3.5 Gammaridea Amphipod - Onisimus sp. 7 -21.2 0.5 10.2 0.5 36.3 2.1 14.5 0.9 40.1 Pteropod - Cliona limacina 8 -25.6 0.3 10.3 0.2 103.3 4.4 29.5 0.9 28.5 Pteropod - Limacina helicina 7 -23.1 0.3 9.3 0.1 96.8 5.3 Hyperiidea Amphipod - Hyperoche sp. 3 -20.2 2.3 13.8 0.1 85.5 11.4 66.1 77.3 Fish larvae - Boreogadus saida 4 -23.3 0.4 10.7 0.4 66.5 6.5 21.6 0.7 32.5 Euphausiacea - Thysanoessa sp. 2 -22.7 2.7 9.4 0.8 36.3 4.1 8.6 23.6 Western Chaetognatha - Sagitta sp. 9 -25.6 3.1 12.2 2.3 25.5 0.6 15.0 0.2 58.7 Arctic Copepod Calanoid - Calanus sp. 8 -28.6 2.8 10.4 0.8 23.3 5.6 10.1 3.5 44.8 Copepod Calanoid - Euchaeta sp. 8 -26.9 1.6 13.1 1.2 81.3 31.3 44.3 2.4 54.9 Hyperiidea Amphipod - Themisto sp. 6 -25.8 1.8 11.7 1.5 65.5 21.1 33.2 14.4 51.9 Pteropod - Cliona limacina 8 -24.9 3.1 11.0 0.0 86.0 4.1 Pteropod - Limacina helicina 7 -24.9 0.3 9.5 0.1 251.0 22.3 19.1 7.6 Hyperiidea Amphipod - Hyperoche sp. 4 -22.7 0.4 16.3 0.0 125.3 19.4 96.5 77.0 Fish larvae - Boreogadus saida 5 -26.3 0.9 11.1 0.1 40.4 1.6 Euphausiacea - Thysanoessa sp. 5 -26.1 0.5 11.0 0.2 20.6 2.2 2.7 13.3
134 135