The Modern Organic Carbon Cycle in Hudson Bay, an Arctic Coastal Sea Undergoing Change
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The Modern Organic Carbon Cycle in Hudson Bay, An Arctic Coastal Sea Undergoing Change by Zou Zou Anna Kuzyk A Thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in partial fulfilment of the requirements of the degree of Doctor of Philosophy Deparlment of Environment and Geography University of Manitoba Winnipeg, Manitoba, Canada Copyright O 2009 by Zou Zou Anna Kuzyk THB UNIVBRSITY OF MANITOBA FACULTY OF GRADUATE STUDIES COPYRIGHT PBRMISSION The Modern Organic Carbon Cycle in Hudson Bay, An Arctic Coastal Sea Undergoing Change By Zou Zou Anna Kuzyk A Thesis/PI'acticum submitted to the Faculty of Graduate Stutlies of The University of Manitoba in partial fulfillment of the requirement of the degree of Doctor of Philosophy ZouZou Anna KuzykO2009 Permission has been granted to theUniversityof Manitoba Libraries to lencl a copyof this thesis/practicum, to Library antl Archives Canada (LAC) to lend a copy of this thesis/practicum, and to LAC's agent (UMlÆroQuest) to microfilm, sell copies and to publish an abstract of this thesis/practicum. This reprocluction or copy of this thesis has been macle available by authority of the copyright ovvner solely for the purpose of private study and researclr, ancl may only be reproducetl and õpied as permitted by copyright lalvs or rvith express rvritfen authorization from the copyright owner. Abstract Arctic coastal seas are important sites of organic carbon cycling. Projected changes in Arctic temperatures, dver inflows and sea ice conditions will affect this cycling, with consequences for local ecosystems and global carbon cycles. To predict and measure the effects of change requires in-depth understanding of organic matter (OM) sources and processes controlling production, transport and burial. In this thesis, various geochemical tools were applied to study the modern organic carbon cycle in Hudson Bay, alarge but poorly-known Arctic inland sea, which is undergoing change more rapidly than other Arctic areas. Organic compositional data for sediments and suspended particulate samples from marine and river waters, together with a biogeochemical box model for nitrate, revealed that new marine primary production is concentrated in inshore surface watets, where there is increased upwelling of deep, nutrient-rich waters. This is probably supported in part by nutrient entrainment related to the large volume of river inflow to the Bay, which circulates through the inshore region. River inflow also provides the largest source of allochthonous (terrigenous) OM. Bulk (C/Ìrtr, ðr3C, ðr5N¡ and specific organic biomarkers (lignin) showed that heterogeneous terrestrial materials undergo hydrodynamic sorting in the coastal zone, resulting in the coarse fraction being retained near river mouths while a fine fraction undergoes transport by marine currents. Seasonal sea ice cover interacts with winter/spring river inflow to influence OM production and transpott indirectly. Sediment and particulate organic carbon budgets showed that resuspension and lateral transport of fine-grained coastal sediments is also an important process, supplying most of the sediment for contemporaly burial of OM and as much terrigenous OM as river inflow and subaerial coastal erosion combined. Resuspension also supplies offshore Hudson Bay with old (glacigenic) marine carbon, supporting slightly enhanced burial of marine OM in the Bay's sediments, compared to other Arctic shelves. The importance of resuspension likely reflects the exceptional postglacial isostatic rebound (relative sea-level fall) ongoing in Hudson Bay. Hypothesized transitional sedimentary and OC regimes in Hudson Bay pose challenges for interpreting responses to climate change and using Hudson Bay as a sentinel for change in Arctic coastal seas. Acknowledgements First, I would like to thank my supervisors, Dr. Robie Macdonald and Dr. Gary Stern, and ArcticNet, for providing me with the incredible opportunity to work in Hudson Bay, and allowing me the freedom to take the research in my chosen direction. I also thank my supervisors for their mentorship and laying before me the challenge of pursuing good science and writing good papers; and for their patience and encouragement. I am grateful to Dr. Macdonald for his generosity with his knowledge of organic carbon cycling and the Arctic Ocean, for his efforts to train me to be a better scientist, and for debating with me about the game of science. I also benefited greatly from the mentorship of Dr. Miguel Goñi and Dr. Christine Michel, and from good science discussions with my committee members (Dr. Michel, Dr. Tim Papakyriakou, Dr. David Lobb) and Mats Granskog, Greg McCullough and Alex Hare. I thank Monica Pazerniuk, teamZAM, Mary o'Brien, cJ Mundy, Johannie Martin, the officers and crew of the ccGS Amundsen, Churchiil community members, and fellow ArcticNet scientists for assistance and support with field work. E. slavicek, M. soon, Y. Alleau, and B. LeBlanc are thanked for laboratory support and P. Kimber for assistance with figures. Financial support from the Natural Sciences and Engineering Research Council of Canada O{SERC), the Northern Scientific Training Program (Indian and Northern Affairs), the Province of Manitoba and the University of Manitoba is gratefully acknowledged. Finally, I would like to thank my grad room buddies, other good friends in Winnipeg and beyond, my family in Ontario, and especially Jason Stow. 111 Table of Contents Abstract.... ................ i Acknowledgements.... .............. iii Table of Contents ..................... iv List of Figures............. ............. vi List of Tab1es............. ................x List of Copyrighted Material for which Permission was Obtained................................... xi Thesis Format and Manuscript Claims................ ........ xi Chapter 1 : General Introduction............... ....................1 Motivation and Thesis Objectives ............. 1 8ackground............... ............... 6 Outline of Thesis Chapters .... 16 References ............ 18 Chapter 2 : Sea lce, Hydrological, and Biological Processes in the Churchill River Estuary Region, Hudson 8ay........... ...................31 Abstract.... ............31 Introduction................ ............32 Materials and methods................ ............. 35 Results...... ............43 Discussion ............62 Conclusions................ ............71 References ............73 Chapter 3 : Sources, Pathways and Sinks of Particulate Organic Matter in Hudson Bay: Evidence from Lignin Distributions.......... .........80 Abstract.... ............ 80 Introduction................ ............ 81 Methods ............... 85 Results...... ............91 Discussion .......... 104 Summary and implications......... ........... 118 References ..........121 Chapter 4 : Toward a Sediment and Organic Carbon Budget for Hudson Bay..............131 Abstract.... .......... 131 Introduction................ .......... 132 Overview of the Hudson Bay System ....134 Methods ............. 138 Results and Discussion .......... ................ 150 References ..........182 1V Chapter 5 : Elemental and Stable Isotopic Constraints on River Influence and Patterns of Nitrogen Cycling and Biological Productivity in Hudson Bay ..............................196 Abstract.... .......... 196 Introduction................ ..........I97 Study area .......... ..................201 Methods .............203 Results and Discussion.......... ................209 References ..........234 Chapter 6: General Discussion and Conclusions......... ...............246 Marine primary production and its controls ............251 Terrigenous OM: sources, composition and distribution ...........257 Role of resuspension. ...........260 Sediment accumulation and OM burial ...................262 Implications for Hudson Bay's responses to climate change ....265 References ..........269 List of Figures Figure 1-1. Location of Hudson Bay and the Arctic Ocean shelf seas. ......... 4 Figure 2-1. Layout of sampling sites (circles) in the Churchill study area and general ice conditions (March-May 2005) .....36 Figure 2-2.Tidal elevations in Churchill Harbour, air temperatures in Churchill, and Churchill River discharge (solid line) and temperature (dashed line) measured at the weir over the five main sampling periods (winter, pre-melt, early melt, peak flow and break up). Black symbols show specific sampling dates. ................44 Figure 2-3. Evolution of the (A) landfast ice edge off the Churchill River, showing where rubble ice was lost during the peak flow (white arrows), and the fast ice then ablated in the break up (black arrow) and (B) surface reflectance, largely a function of open water, in the Churchill River estuary. Images are modified from A) Quickbird RGB composites, May 16 and27, and B) MODIS "MOD09GQK" BAND 2, Aprll?7,May 16, May 29............. .....47 Figure 2-4. Salinity profiles for Button Bay and El under the ice in the pre-melt, early melt and peak flow periods (spring 2005) and in open water in the fall of 2005..... 50 Figure 2-5. ôl80 - salinity relationships for water samples from the Churchill estuary region (a) and ôr8O profiles for ice cores from the estuary area (April 8 at E1, solid square, May 19 at T3, open squffe) and Button Bay (April 6, solid triangle and May 5, open triangle) (b) .... ... ..............52 Figure 2-6. Seasonal trends in surface water salinity in Button Bay and the estuary region (El and T3) derived from ice core records of ðr80. ....................52