Late Quaternary dinoflagellate cyst stratigraphy at the Eurasian continental margin, Arctic Ocean: indications for Atlantic water inflow in the past 150,000 years

Abstract. Late Quaternary paleoceanographic changes in the central Arctic Ocean were reconstructed from a multicore and gravity core from the Lomonosov Ridge (Arctic Ocean) collected during the 2014 SWERUS-C3 Expedition. Ostracode assemblages dated by accelerator mass spectrometry (AMS) indicate changing sea-ice conditions and warm Atlantic Water (AW) inflow to the Arctic Ocean from ~ 50 ka to present. Key taxa used as environmental indicators include Acetabulastoma arcticum (perennial sea ice), Polycope spp. (productivity and sea ice), Krithe hunti (partially sea-ice free conditions, deep water inflow), and Rabilimis mirabilis (high nutrient, AW inflow). Results indicate seasonally sea-ice free conditions during Marine Isotope Stage (MIS) 3 (~ 57–29 ka), rapid deglacial changes in water mass conditions (15–11 ka), seasonally sea-ice free conditions during the early Holocene (~ 10–7 ka) and perennial sea ice during the late Holocene. Comparisons with faunal records from other cores from the Mendeleev and Lomonosov Ridges suggest generally similar patterns, although sea-ice cover during the last glacial maximum may have been less extensive at the southern Lomonosov Ridge at our core site (~ 85.15° N, 152° E) than farther north and towards Greenland. The new data also provide evidence for abrupt, large-scale shifts in ostracode species depth and geographical distributions during rapid climatic transitions.

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Atlantic Water properties, transport, and water mass transformation north of Svalbard from one-year-long mooring observations

10.5194/egusphere-egu21-2505 ◽

2021 ◽

Author(s):

Zoé Koenig ◽

Kjersti Kalhagen ◽

Eivind Kolås ◽

Ilker Fer ◽

Frank Nilsen ◽

...

Keyword(s):

Arctic Ocean ◽

Water Layer ◽

Atlantic Water ◽

Water Inflow ◽

The Arctic ◽

Short Time Scale ◽

The Arctic Ocean ◽

Explained Variance ◽

One Year ◽

Counter Current

North of Svalbard is a key region for the Arctic Ocean heat and salt budget as it is the gateway for one of the main branches of Atlantic Water to the Arctic Ocean. As the Atlantic Water layer advances into the Arctic, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate around the Arctic Ocean.In September 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for more than one year (until November 2019), within the framework of the Nansen Legacy project to investigate the seasonal variations of this current and the transformation of the Atlantic Water North of Svalbard. The Atlantic Water inflow exhibits a large seasonal signal, with maxima in core temperature and along-isobath velocities in fall and minima in spring. Volume transport of the Atlantic Water inflow varies from 0.7 Sv in spring to 3 Sv in fall. An empirical orthogonal function analysis of the daily cross-isobath temperature sections reveals that the first mode of variation (explained variance ~80%) is the seasonal cycle with an on/off mode in the temperature core. The second mode (explained variance ~ 15%) corresponds to a short time scale (less than 2 weeks) variability in the onshore/offshore displacement of the temperature core. On the shelf, a counter-current flowing westward is observed in spring, which transports colder (~ 1&#176;C) and fresher (~ 34.85 g kg-1) water than Atlantic Water (&#952; > 2&#176;C and SA > 34.9 g kg-1). The processes driving the dynamic of the counter-current are under investigation. At greater depth (~1000 m) on the offshore part of the slope, a bottom-intensified current is noticed that seems to covary with the wind stress curl. Heat loss of the Atlantic Water between the two mooring arrays is maximum in winter reaching 250 W m-2 when the current is the largest and the net radiative flux from the atmosphere to the ocean is the smallest (only 50 W m-2 compared to about 400 W m-2 in summer).

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