Paleoecological Reconstruction of the Late Tyrrell Sea Phase at Old Factory Lake, Eastern James Bay, Québec Pendea I. F.*, Costopoulos, A.**, Pospelova, V.***, Chmura, G. L.* *Department of Geography & Global Environment and Climate Change Centre, McGill University, QC **Department of Anthropology, McGill University, QC ***School of Earth & Ocean Sciences, University of Victoria, BC N

Brigantedinium spp.

Introduction Recent archaeological surveys in the area around Old Factory Lake, east of James Bay (Fig 1) have revealed coastal settlements indicating higher than expected density of occupation and lower than expected mobility of early human populations. Burnt seal bones found at the site (Fig 2) imply that marine resources, likely associated with the Tyrrell Sea, were an important food source for this settlement. Near the archaeological site we located the former Tyrrell sea bed and report on our paleoecological reconstruction of the former marine environment, asking if marine resources would have been a significant food source. Previous studies of early Holocene deglaciation of eastern James Bay infer that the Tyrrell Sea flooded the area as early as 8 ka BP, 8.7 ka cal BP, (1). Isostatic uplift forced a rapid retreat of the sea. The Old Factory Lake basin became free of marine influence probably between 6 and 5 ka cal BP (2).

Hudson Bay

Nouveau Québec Islandinium minutum

Old Factory Lake

Methods

Results

• 20 cm-long core from the buried relict sea bed was analyzed for dinoflagellate cysts & pollen. • A minimum of 422 cysts identified using published taxonomic descriptions (3, 4, 5).

•13 cyst morphotypes from 7 genera (Fig 3). •Spiniferites spp. dominant (40-60%). •high abundances of P . dalei, O. centrocarpum and S. ramosus.

James Bay

A

Open paleo-bay

B

Isolation phase (late Tyrrell Sea phase)

C

Present Old Factory Lake

Spiniferites mirabilis

100 km

Fig. 1. Location map Scale 1:400 000

Old Factory Lake paleo-bay

Core site

Scale 1:400 000

Scale 1:400 000

Fig. 4 Shoreline displacement simulation using a Digital Elevation Model (DEM).

Archaeological site with burnt seal bones

Discussion Non-analogue Assemblage The dinoflagellate assemblage is dominated by autotrophic taxa up to 99%. There is no apparent modern or fossil analogue assemblage, but Spiniferites spp. is well represented in modern assemblages from the Norwegian west coast (6) and some similarities exist with early Holocene assemblages from the same region, e.g., codominance of P. dalei, Spiniferites spp. and O. centrocarpum (7).

shallows

Tyrrell Sea

Fig. 2 Simulated coastal configuration prior to the isolation of the lake basin. Fig. 3. Dinocyst diagram.

Spiniferites spp.

Spiniferites ramosus

A Shallow Embayment Modern cyst assemblages from northern James Bay are dominated (up to 95%) by the cosmopolitan subarctic P. dalei (8) where sea surface temperature (SST) is ~7ºC and has varied little during the Holocene (9). In the Old Factory Lake assemblage (Fig 3) the abundance of cold water taxa (e.g., P. dalei) is much lower (10-28%) and more temperate taxa (e.g., Spiniferities spp.) are more abundant. In particular, the occurrence of Spiniferites mirabilis suggests a SST warmer than today. This could reflect local conditions of the Tyrrell Sea coast, namely, a semi-enclosed shallow embayment (Fig. 4B) which would have reached higher temperatures in summer and been affected by increased thermal influence from the surrounding landmass. The presence of shallow sea water is also indicated by up to 1.4% Ruppia (a submerged aquatic) pollen. The shoreline displacement simulation based on the digital elevation model (Fig 2) also suggests the presence of shallows during the isolation phase. Nutrient Poor Water The Spiniferites group (S. spp., S. ramosus & S. mirabilis) is negatively correlated (R>0.5) with February nitrates and phosphates (10). Therefore, the Spiniferitesdominated assemblage at Old Factory Lake is indicative of nutrient-poor sea water in spring and, potentially, low primary productivity. Cyst influx can reflect production and will be calculated when carbon-14 dating and sedimentation rates are available. Salinity Abundances of P. dalei and O. centrocarpum indicate that in the Old Factory paleo-bay water salinity was 25-35 PSU, based upon observations from modern samples from the northern North Atlantic (11). The inferred salinity for the Old Factory paleo-bay is higher than modern salinities on James Bay coast (0-27 PSU).

Selenopemphix quanta

Operculodinium centrocarpum var. truncatum

Impagidinium aculeatum

Conclusions •Seal bone fossils found in the archeological site could suggest that marine resources were important. However, the nutrient-poor nature of the marine water inferred from the dinoflagellate cyst assemblage does not support an interpretation of abundant marine resources. X10* X10*

X10*

* exaggeration

Dots=<0.5%

•Future work will try to document if perhaps widespread coastal wetlands – major habitats for waterfowl and other game, were present on the shores of the Tyrrell Sea Bay, which could offer an alternative explanation for the unusual type of human presence in the area.

Fig. 3. Dinoflagellate cyst diagram from Old Factory Lake.

References 1. Hardy, L. (1982) Naturaliste canadien, 109, 333-351. 2. Dyke, A. S. et al. (2003) Geological Survey of Canada, Open File 1574, Ottawa. 3. Mudie, P.J. (1992) Neogene and Quaternary Dinoflagellate cysts and Acritarchs, pp.347-390, Dallas. 4. Rochon, A. et al. (1999) Distribution of recent dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters, Dallas, 152 pp. 5. Head, M.J. et al. (2001) Journal of Quaternary Science, 16, 621-636.

6. Grøsfjeld, K. & Harland, R. (2001) Journal of Quaternary Science, 16, 651-659. 7. Grøsfjeld, K. et al. (1999) Boreas, 28, 403-415. 8. Mudie, P.J. & Rochon, R. (2001) Journal of Quaternary Science, 16, 603-620. 9. de Vernal, A. & Hillaire-Marcel (2006) Global and Planetary Change, 54, 263-290. 10. Devillers, R. & de Vernal, A. (2000) Marine Geology, 166, 103-124. 11. de Vernal, A. et al., (2001) Journal of Quaternary Science, 16, 681-698.

Acknowledgements This research is funded under the European Science Foundation Eurocores BOREAS: Histories from the North Program, with SSHRC, NSF and the Finnish Academy; with additional support from NSERC and the Community-University Research Alliance (CURA). Colin Nielsen provided figures derived from digital elevation model.