Periodic Reporting for period 1 - POLARC (High Arctic Polynyas in a Changing Climate)
Période du rapport: 2019-07-15 au 2021-07-14
The Arctic region is experiencing the impact of varying climatic conditions more keenly and rapidly than elsewhere on the planet. Declining Arctic sea-ice extent and thickness have direct impacts along the coast of Greenland, where the Arctic Ocean connects to the wider North Atlantic circulation via the gateways of the Nares and Fram Straits. Within the largely sea-ice dominated coastal waters of Greenland, areas of open water i.e. polynyas, sustain enhanced biological production. The largest high Arctic polynya, the North Water in northernmost Baffin Bay, is highly sensitive to climate forcing; it’s viability as a hotspot of primary productivity was impacted by rapid warming and cooling trends characterising the current Holocene epoch (last 11,700 years) and its formation mediated northward transport of warmer waters from the south. One of the objectives of this project was to return to these records and apply geochemical analysis to estimate quantitative bottom water temperature changes. Unlike its western Greenland counterpart, virtually nothing is known of the history of the Sirius Water Polynya that recurrently forms at 74 degrees north on the North-East Greenland coast, although archaeological evidence implicates the polynya as a driver of human occupation in the area over the last 4,500 years. The main objective of this project was to apply different methodologies to one of the first marine sediment cores in this region to track the evolution of primary productivity as well as surface and bottom water conditions throughout the last 12000 years.
To reconstruct conditions throughout the water column at the site of the Sirius Water polynya several types of analysis were conducted on discrete one-centimetre slices of sediment. Changes in primary productivity were ascertained using measurements of organic carbon and nitrogen, as well as biogenic silica content of the sediments. The latter indicates levels of (diatom) primary production, an important ecosystem function in polynya settings and the analyses represented a new skill for the researcher. Benthic (bottom dwelling) foraminifera, whose calcareous shells are preserved as fossils in marine sediments, were counted and as different species have different environmental preferences inferences were made about the bottom water conditions in which they lived. The age of the sediment was established using radiocarbon dating of these same shells and indicated that these marine sediments were deposited between 0 – 12000 years ago. The amount of sediment deposited in the earlier part of the record was much larger and from 12000 to 7500 years ago, that translates to sub-centennial resolution of reconstructions. Conditions changed rapidly at the transition between the previous Younger Dryas cold period, that lasted until 11,700 years before present, and the current Holocene warm epoch. This multi-proxy study will be published in a peer-review manuscript to evaluate the impact of wider Arctic and North Atlantic Ocean circulation and atmospheric regimes on the evolution of marine conditions on the North-East Greenland shelf.
For the North Water polynya marine sediment core, a specific benthic foraminifera species was extracted from samples. The stable oxygen isotopic signature contained in these shells reflects the salinity and temperature of the water masses in which the shells were formed. The ratio of magnesium to calcium in the shells reflects primarily water temperature and using a species-specific calibration, these ratios can be transformed into water temperature. This quantitative analysis will also be published in a peer-review article and builds on qualitative work already completed. The results will be used to compare past time intervals when it is known that polynya formation was strong (or weak) and the impact this may have had on ocean circulation and ocean heat transport into northern Baffin Bay.
For the North Water polynya marine sediment core, a specific benthic foraminifera species was extracted from samples. The stable oxygen isotopic signature contained in these shells reflects the salinity and temperature of the water masses in which the shells were formed. The ratio of magnesium to calcium in the shells reflects primarily water temperature and using a species-specific calibration, these ratios can be transformed into water temperature. This quantitative analysis will also be published in a peer-review article and builds on qualitative work already completed. The results will be used to compare past time intervals when it is known that polynya formation was strong (or weak) and the impact this may have had on ocean circulation and ocean heat transport into northern Baffin Bay.
The reconstructions from the Sirius Water polynya are novel in that it is the first high resolution marine record from this part of the North-East Greenland coast. Unlike other marine records to the north, it extends back into the Younger Dryas thus covering the transition from a cold period to the current Holocene warm period. Its location is far afield from both the large marine terminating glaciers that flank the Greenland coast and the major pathways of Atlantic Water onto the North-East Greenland shelf. This makes it an excellent location to track changes in the Arctic Ocean, their propagation south via the East Greenland Current and the impact this had on potential polynya formation, marine ecosystems, and ocean conditions back through time.
The reconstructions of bottom water temperatures in the North Water Polynya represent the first attempt at using this methodology in a Greenland polynya region. They make use of recently published species-specific calibrations that extend the lower limits of the temperature range in the polar regions. Informed by the qualitative work already done on the same marine records, the quantitative nature of data means ranges of temperature change in different climatic and polynya regimes can be established. Furthermore, this data could be incorporated into regional climate models to potentially tune future climate simulations. As an already identified climate risk, a proposed UNESCO site of enormous historical and societal value to indigenous peoples, accurate predictions of climate change impacts are vital for the North Water polynya region.
The reconstructions of bottom water temperatures in the North Water Polynya represent the first attempt at using this methodology in a Greenland polynya region. They make use of recently published species-specific calibrations that extend the lower limits of the temperature range in the polar regions. Informed by the qualitative work already done on the same marine records, the quantitative nature of data means ranges of temperature change in different climatic and polynya regimes can be established. Furthermore, this data could be incorporated into regional climate models to potentially tune future climate simulations. As an already identified climate risk, a proposed UNESCO site of enormous historical and societal value to indigenous peoples, accurate predictions of climate change impacts are vital for the North Water polynya region.