Enhanced Arctic stratification in a warming scenario: Evidence from the mid pliocene warm Pperiod

Global warming is most pronounced in the Arctic as evident from the massive sea ice loss during the past few decades. The Mid-Pliocene Warm Period (MPWP), 3.264 – 3.025 million years ago with similar CO2 levels, is the nearest analogue for understanding the impacts of future global warming. High-resolution studies of relative nutrient utilization and productivity from the Atlantic-Arctic Gateway (AAG) can provide insight into the nutrient availability governed by stratification strength during past warm climates. Here, we present relative nutrient utilization and productivity variability during the MPWP using sediments collected during the Ocean Drilling Program (ODP) Leg 151 from Fram Strait, AAG. We find that the relative nutrient utilization was high (low) implying stronger (weaker) stratification during warm (cold) periods during the MPWP. Stronger stratification inhibits the nutrient influx from intermediate water depths into the surface leading to higher utilization of available nutrients. It existed during warm periods likely due to enhanced summer sea ice melt and river discharge from the hinterland. As a consequence, the freshened surface layer could have stored more heat and accelerated the sea ice melt further implying that in the present-day warm scenario, stronger stratification and upper layer freshening may lead to more sea ice melt in the Arctic Ocean

Enhanced Arctic Stratification in a Warming Scenario: Evidence from the Mid Pliocene Warm Period

This paper was published by AGU. Copyright (2021) American Geophysical Union.Global warming is most pronounced in the Arctic as evident from the massive sea ice loss during the past few decades. The Mid-Pliocene Warm Period (MPWP), 3.264 – 3.025 million years ago with similar CO2 levels, is the nearest analogue for understanding the impacts of future global warming. High-resolution studies of relative nutrient utilization and productivity from the Atlantic-Arctic Gateway (AAG) can provide insight into the nutrient availability governed by stratification strength during past warm climates. Here, we present relative nutrient utilization and productivity variability during the MPWP using sediments collected during the Ocean Drilling Program (ODP) Leg 151 from Fram Strait, AAG. We find that the relative nutrient utilization was high (low) implying stronger (weaker) stratification during warm (cold) periods during the MPWP. Stronger stratification inhibits the nutrient influx from intermediate water depths into the surface leading to higher utilization of available nutrients. It existed during warm periods likely due to enhanced summer sea ice melt and river discharge from the hinterland. As a consequence, the freshened surface layer could have stored more heat and accelerated the sea ice melt further implying that in the present-day warm scenario, stronger stratification and upper layer freshening may lead to more sea ice melt in the Arctic Ocean

Oxygen isotope-salinity relation in an Arctic fjord (Kongsfjorden): Implications to hydrographic variability

The global warming leads to a large freshwater influx into the Arctic Ocean, which has adverse implications to the sea-ice dynamics, ocean circulation, and acidification. The relationship between oxygen isotope ratio (δ18O) and salinity (S) is helpful in exploring various hydrographic processes related to the freshwater influx and is also required to accurately determine past salinity variability using oxygen isotope ratio of the carbonates. In view of this, systematic measurements of δ18O and salinity of water from an Arctic fjord (Kongsfjorden) were carried out during the summer season of 2013. Until now, the relationships between δ18O and salinity from such fjords were based on a limited number of samples collected during a very short span of time and thus may not accurately represent the long-term conditions prevailing in the fjord. The present study determines a more representative δ18O–salinity relationship as water samples from different depths and location over a long period were systematically collected. The water samples were collected from four different locations at different depths along the axis of the fjord representing the inner and outer fjords. The inner stations (I-8 and I-6) exhibit lower δ18O values than the outer stations (I-1 and I-3), which indicate the higher influence of freshwater from glacial melting in the inner stations. The δ18O–salinity relationship from the inner and outer fjords yield a slope of 0.54 (r2 = 0.67, n = 56) and 0.39 (r2 = 0.66, n = 68), respectively. The δ18O of freshwater influx in the fjord is estimated at –18.4‰, which is close to the widely accepted freshwater-δ18O value of the Arctic basin. The δ18O of glacial discharge, which is the largest source of freshwater influx to the fjord, is estimated at ca. –21.0‰, which will be useful for future freshwater budget calculations. Keywords: Arctic, Fjord, Oxygen isotopes, Salinity, Freshwater, Meltin

Paleoenvironment Variability during Termination I at the Reykjanes Ridge, North Atlantic

The micropaleontological study (radiolarians and foraminifera) of the sediment core AMK-340, Reykjanes Ridge, North Atlantic, combined with the radiocarbon dating and oxygen and carbon isotopic record, provided data for the reconstruction of the summer paleotemperature across the upper 100 meters water depth range, and paleoenvironments during the Termination I in the age interval of 14.5–8 ka. The response of the main microfossil species to the paleoceanographic changes within the Bølling-Allerød (BA) warming, the Younger Dryas (YD) cold event and final transition to the warm Holocene, was different. The BA warming was well captured by the radiolarian and benthic foraminiferal records, but not the planktic one. The high abundances of the cold-water radiolarian species Amphimelissa setosa as a Greenland/Iceland Sea indicator marked a cooling at the end of the BA and at the start of the YD at 13.2–12.3 ka. The micropaleontological and isotopic data together with the paleotemperature estimates for the Reykjanes Ridge at 60°N document that, after the warm BA, the middle YD ca. 12.5–12.2 ka was the next significant step toward the Holocene warming. The start of the Holocene interglacial conditions was reflected in large representation of the microfossils being indicators of the open boreal North Atlantic environments indicating increasing warmth