DISTRIBUTIONS OF FORAMINIFERA OVER THE LAST 15,000 YEARS INCLUDING STABLE ISOTOPIC DATA FROM THE BEAUFORT SLOPE, BEAUFORT SEA, CANADA: IMPLICATIONS FOR PAST SEA-ICE CONDITIONS David Scott and Trecia Schell,Dalhousie University, Department of Earth Sciences and André Rochon, Universitè à Quebec à Rimouski,PQ. David Scott,Trecia Schell, Dalhousie University, Earth Sciences André Rochon, Guillaume St. Onge Universitè à Quebec à Rimouski, Jennifer Mackay,UQaMontreal Dennis Darby, Old Dominion Univ.
Beaufort Shelf
Study area Core 750 1000m WD Core 124 350m WD MODIS 29 AUGUST 2001
Coring at the edge of the Arctic Ice pack - Beaufort Sea In 1000m
Sample Collection All cores are archived at the Bedford Institute of Oceanography,, NS in the ED-at at-sea database, which will soon be accessible through the Internet CASES 2003-2004: 2004: 44 boxcores + 7 piston cores PC750 Piston core 650 850 750 PC124 850
Seismic line across the PC 750 site - because of ice conditions at the time, we could not obtain any reasonable multibeam images. However it appears from the seismic that at least the upper few meters were not slump deposits
Rhizammina algaeformis Baculella cf. globofera High # s of calcareous, small deep-sea forms forms at the surface - replaced by agglutinated forms below 2cm, except Bolivina arctica (calcareous), And below 13cm, the fauna is pyritized Komokiacea
A deformed Planktonic foram! Cribrostomoides crassimargo Similar to <63mic except that calcareous species are different, especially Planktics, of which many are not normal
In 1970 during the Hudson cruise the ice was over 100 miles offshore, beyond the 3900m contour. This core was at the ice edge in 1000m of water 1970? Lead 210 Pb and 137 Cs suggest this interval is less than 100yBP. X-radiograph The layering below is contains the pyritized forams, indicating reducing conditions & high OC. The highest OC, occurs in the 10-15cm interval - the distinct layers also appear in the x-ray images ( 210 Pb by Amiel and Cochran-SUNY)
11,600calBP 13,500calBP Dates are from sections with the most forams-for the small Native Arctic forms(in boxes), almost all specimens are between 45 and 63mic
250-270cm 270-285cm Core PC750 X-rays 210-230cm 230-250cm Ice rafted 11,600calBP Abundant forams 136-150cm 190-210cm 150-170cm 100-120cm 120-136cm
Beaufort Sea Mckenzie Trough 1000m contour Beaufort Shelf Piston Core 124 Mckenzie Delta Core 124 Amundsen Gulf Drumlin-like features are 60m high and 10km long Ice rafted Sediments In core from Site 124 at The 1.3 m depth Dated at 12,600calBP These images Illustrate The former Ice margin In Amundsen Gulf as it Tapers off To where The ice Stopped just South of Core 124 in Over 400m Of water
Multibeam near stations 106-118 12,620calBP 12,650calBP >35,000ybp Freshwater Peat As with PC 750 the majority of the native Arctic species Are in the 45-63mic fraction
PCCore 124 60-220cm 90 to 180cm The C-14 dates suggest that the glaciers in Gulf moved in the time between the core 750 IRD 180-200cm 200-220cm 140-160cm 160-180cm 100-120cm 120-140cm 60-80cm 80-100cm
0 cm 100 200 300 Magnetic Susceptibility Mean grain (x10-6 S) CT# ARM(30mT) IRM(30MT) IRM/SIRM(SI) Size(µm) mm 996 1004 2 4 6 0 400 500 0 2 10-2 0 0.4 0.8.85.95 1.05 IRD1 IRD2 The magnetic signatures suggest the IRD in both sites have the same source however the ages are very different. The clay mineralogy should answer this question. 400 500 Core 750-paleomag CT# mm 996 1004 Magnetic ARM(30mT) Susceptibility 0.85 1.05 IRM(30MT) IRM/SIRM(SI) (x10-6 -6 S) 0 2x10-5 4x10-5 0 400 600 800 0 0.004 0.008 0.6 0.8 1.0 One source is certainly from the glacier that was in the Amundsen Gulf however that may only be in core 124 since the dates suggest that the 124 IRD event occurred between the two IRD units in core 750. Core 124-paleomag Core 124-paleomag
Isotopes for Both benthics and planktics- Benthics show little change while planktics do vary The benthic 0 18 Values are ~+4/mil From the surface to The bottom of the Core-i.e. same in Both late Holocene And late glacial The planktics are At least +1/mil heavier In the glacial. Carbon Values for O.umbonatus are lower
There was only two intervals with sufficient numbers of Foraminifera for isotopes and only one species, I. teretis. Values were similar to those in PC750
CESAR Ice station site 2500m
CORE 102-1MYA-UNIT L of Clarke et al extends from 50-80cm +4 +3 2 +4 018 Unit L 018 Is unit L actually MS11 which has Been suggested to be an extended Warm period in the mid-quaternary? This is an old figure but it gives a comparison to a deep sea Arctic isotope record for both planktics and benthics
For ice history in the Beaufort Sea the calcareous faunas at the surface of cores 750 and 124 suggest more sea ice in the last 30 years which fits with observations from a CSS Hudson cruise here in 1970 when the ice pack was almost 100km farther out. Fisher et al. (2006, EOS) discuss the presence of much less ice between 8 to 10kybp based on whale remains But it appears that it may have been less extensive much Later at least once in the Beaufort Sea. The isotope record is very similar to the upper part of The CESAR Alpha Ridge cores where the planktic oxygen Isotopes vary between the interglacial and late glacial but Not the benthic ones-this persists for 400,000yrs on the Alpha Ridge suggesting no world ice volume signal in the Arctic Ocean and at least for the last glacial on the Beaufort Shelf region
And thanks, to all of our collaborators & colleagues!
Another exciting day on the Amundsen Any Questions?
Bye, bye!!