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Time Series Foraminiferal Fluxes from the Iceland

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Time Series Foraminiferal Fluxes from the Iceland Dorinda Ostermann (W.H.O.I., Woods Hole, MA 02543; [email protected]), William B. Curry (W.H.O.I., Woods Hole, MA 02543), Susumu Honjo (W.H.O.I., Woods Hole, MA 02543), Jon Olafsson (Marine Research Institute, Reykjavik; [email protected]), Steven J. Manganini (W.H.O.I., Woods Hole, MA 02543; [email protected]) G. quinqueloba N. pachyderma N. pachyderma The Greenland, Iceland and Norwegian Seas (GIN) together form 0.5 0-200 Meter Data dextral (R) sinistral (L) W) a high latitude region with waters of both Arctic and North Atlantic 18 Iceland Sea Water Temperature (°C), 1986-1999 (SMO Relationship between salinity (psu) and the δ O (SMOW) origin mix. The GIN Seas have also been recognized as critical to 86 87 88 89 90 91 92 93 94 95 96 97 98 99 content of the upper 200 meters of water around Iceland 0 8.8 water based upon Geosecs (> 60°N) and water collected around the formation of North Atlantic Deep water (NADW) whose produc- O 18 0.0 Iceland by D.R. Ostermann and extracted and measured -50 δ Location of sediment trap mooring at Harvard University by D. Schrag. tion has been linked to the heat balance associated with the Global ° (68°N, 12.6°W) indicated by Geosecs >60 N -100 Iceland Plateau 1995 & 1997 Conveyor circulation system. The Iceland Sea sediment trap was yellow star, showing basin and West Iceland (64.3°N 28.8°W) bottom topography. ater Depth (m) 2.0 ° ° deployed to monitor the particle flux response to decadal changes W -150 East Iceland (64.5 N 6 W) 1.0 Time series temperature and salinity profiles -0.5 0.0 in local and regional hydrographic conditions and to interpret down- of the upper 200 meters of water at the 34.0 34.5 35.0 35.5 -200 -1.2 Iceland Sea Oxygen Isotopes, 1994-1996.5 mooring location. This figure is based upon Salinity (psu) Iceland Sea Salinity (psu), 1986-1999 AVHRR satellite sea surface temperature 2 core N. pachyderma and G. quinqueloba flux and stable isotope 86 87 88 89 90 91 92 93 94 95 96 97 98 99 data and data from at least four hydro- 0 34.94 records on glacial to interglacial time scales. graphic bottle casts during each year (data The blue line in each panel at right shows the 34.85 18 3 from the M.R.I., Reykjavik, Iceland). Note average equilibrium calcite δ O of the surface At the Iceland Sea mooring location, in-situ and satellite derived -50 34.79 temperature data and measured δ18O (SMOW) 34.74 the deepening of the fresher water lens 34.70 data from the panel above. The red line in each g (data as collected) 18 sea surface temperature (SST) data show clear interannual oscilla- 34.64 during the years beginning in 1996. 4 Calcite δ O -100 We speculate that this may indicate a panel is the average 150-250 µm G. quinqueloba G. quinqueloba δ18O isotopic measurements. The upper panel shows No La tions between cold and warm periods which have affected the ater Depth (m) deepening of the surface mixed layer Location of Iceland Sea Sediment Trap Mooring, 1986 – present W -150 providing greater nutrient availability. The that foraminiferans are almost 180 degrees out of 2 phase with the equilibrium δ18O. This means that planktonic foraminiferal faunal assemblage and stable isotopic data. 60 bottom figure shows the foraminiferal flux ˚W ˚ E 34.29 the shells were calcified almost 6 months prior to Current diagram showing water 60 30 -200 lagged by 14 days. The width of each bar These dramatic temperature oscillations do not directly affect the ˚W 3 ˚E deposition into the sediment trap. A 6 month "lag" masses affecting the mixture of 30 Year indicates the sampling interval which was g (6 months) water at trap location. -1 86 87 88 89 90 91 92 93 94 95 96 97 98 99 shows foraminifers calcifying in enriched waters timing and magnitude of the peak foraminiferal flux (> 125 µm usually ~27 days. Although rare, N. pachy- La ˚N y 10000 Shells Calcifying 80 well before the temperature actually begins to 4 out of equilibrium? 70 da derma dextral (R) occurs at the same time T Iceland Sea Foraminiferal Flux, 1986-1999 2 -1 N Lag too big... Max. E 2 individual foraminiferal tests m day ) which have been ˚ N R warm up, not likely to happen under normal ocean- R as N. pachyderma sinistral (L) at this U C D 8000 ographic conditions. With a "lag" of 3 months, G. N A location. L documented to occur in almost any month at this location. N 2 E quinqueloba data are brought into phase with the E R G GREENLAND . Greenland E Greenland surface δ18O. G. quinqueloba was used to set the Sea 6000 The 1998-1999 collection interval clearly shows an earlier and T N lag because as a surface dweller, its shell chemistry E 3 Labrador R R g (3 months) Sea U 18 LABRADOR Sea C exhibits a strong seasonal sea surface δ O signal greatly intensified spring bloom, more typical of the North Atlantic C 4000 I D N m individual tests m (see panel below). A Shells Calcifying µ L E in equilibrium than the summer and fall blooms of the Iceland Sea. Although the C 4 NEWFOUNDLAND I Norwegian . E Sea 2000 Optimal La T foraminiferal faunal assemblages contain similar species during the N E R 94.0 94.5 95.0 95.5 96.0 96.5 R Flux >125 Year CU N entire 1986-1999 collection interval, the foraminiferal flux collected 50 IA ˚ EG 60˚N µ N W Peak >125 m Foraminiferal Flux OR G. quinqueloba N. pachyderma (R) N. pachyderma (L) N tests/m2/day during 1998-1999 is more indicative of a North Atlantic bloom sig- N 0 4000 8000 12000 16000 OR 125-150 125-150 125-150 TH nature. Olafsson et al. (see poster to the left) document a greatly ATL NT North Denmark Strait ANTIC CURRE IRELAND 40 150-250 150-250 150-250 ˚N Iceland Sea 1986-1997 increased total particulate flux for this interval. These particle fluxes 13 glass balls Modified from McCartney et al., 1996. Oceanus, vol. 39(2). A compilation of foraminiferal fluxes from sedi- Iceland Sea 1998-1999 for flotation may correlate with a westerly inflow of warmer nutrient-rich Atlantic ment traps deployed around the world. Iceland South Iceland G. quinq ueloba 3 Month Lag N. pachyderma Left & Right 3 Month Lag 91 cm dia. 2 2 Sea peak fluxes were averaged from 1986-1997 JGOFS 47 North water north of Iceland. and presented separately from the 1998-1999 JGOFS 34 North deployment interval. The 1998-1999 Iceland Sea Stable isotopic data indicate that the foraminiferans at the 1423 Sea of Okhotsk mbs peak foraminiferal fluxes are similar in magnitude Iceland Sea mooring location are living for 3-6 months. They make to some of the most productive areas of the world Western Arabian Sea (eg. Arabian Sea, Curry et al., 1992 & Sea of Central Arabian Sea 3 3 their shells in isotopically enriched waters and reproduce, die and Okhotsk, Alderman, 1996). Eastern Arabian Sea O (PDB) settle into the sediment trap 3-6 months later. Poulain et al. North Bay of Bengal 18 δ Side View detail of Central Bay of Bengal (1996) show the mooring location to be in an area of low near- Mk 7-13 Sediment trap Antarctic peninsula surface current velocities and we believe that the oxygen isotopic 152 cm 4 4 Iceland Sea Foraminiferal Weight Flux, 1986-1999 signature of G. quinqueloba indicates in-situ calcification and not Mk 7-13 -1 y 70 Sediment calcification in waters to the south or north with subsequent trans- da Trap C M 2 60 86 87 88 89 90 91 92 93 94 95 96 97 98 99 86 87 88 89 90 91 92 93 94 95 96 97 98 99 port to the mooring location, and deposition into the sediment trap. Year Year g m µ 50 G. quinqueloba oxygen isotopic data plotted with sur- N. pachyderma oxygen isotopic data plotted with sur- The use of stable isotopic analyses allows us to correctly identify face water equilibrium calcite (black line). This species face (black line) and 40 meter (orange line) equilibrium 40 is a surface dweller and show a strong seasonal signal, calcite δ180. This species is a subsurface dweller, living the timing of foraminiferal calcification. with the 125-150 µm individuals living slightly deeper at or near 40 meters during the entire year. 30 than the individuals in the 150-250 µm fraction. eight Flux W References: 430 20 m mab µ 1 10 Alderman, S.E. 1996. Planktonic Foraminifera in the Sea of Okhotsk: Water Masses around Iceland Sea 0 Population and Stable Isotopic Analysis from a Sediment Trap. M.I.T./ 125-150 North Atlantic Current (61°N 27°W) 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 10 -1 70 W.H.O.I. Joint Program in Oceanography, Masters Thesis. pp. 1-99. y Benthos Norwegian Current (68°N 5°W) da C (PDB) Acoustic 2 60 13 Release 8 δ -1 Curry, W.B., D.R. Ostermann, M.V.S. Guptha and V. Ittekkot. 1992. g m 50 µ Foraminiferal production and monsoonal upwelling in the Arabian Sea: 1000 kg Anchor 40 C) N. pachyderma & G. quinqueloba 3 Month Lag ° 6 evidence from sediment traps.
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