An analysis of Atlantic Water in the Arctic Ocean using the Arctic Subpolar Gyre State Estimate and observations

Abstract

The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate (ASTE), a regional, medium-resolution coupled ocean-sea ice state estimate, is analyzed for the first time using bounding isopycnals. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate (2004) and traverses the Arctic Ocean along boundary current pathways at approximately 2 cm/s. The surge also alters AW flow direction and speed including a significant reversal in flow direction along the Lomonosov Ridge. The surge results in a new quasi-steady AW flow from 2010 through the end of the state estimate period in 2017. The time-mean AW circulation during this time period indicates a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A threelayer depiction of ASTE's overturning circulation within the AO indicates AW is converted to colder, fresher Surface Layer water at a faster rate than is transformed to Bottom Water (1.2 Sv vs. 0.4 Sv). Observed AW properties compared to ASTE output indicate increasing misfit during the simulated period with ASTE's AW Layer generally being warmer and thicker than in observations.

Changes in Freshwater Distribution and Pathways in the Arctic Ocean Since 2007 in the Mercator Ocean Global Operational System

“…After 2012, the model showed that dense AW progressively shoaled along the East Siberian Sea slope (Figure 9) until reaching the Mendeleev Ridge by the end of 2017 (Figure 7g). This is in agreement with a previous model‐based study that described the thickening and warming of the AW layer as far as the Mendeleev Ridge in 2010–2017, although no change had been found in the AW layer upper boundary (Grabon et al., 2021). Here, the PSY4 simulations showed that the AW shoaling was accompanied by a weakening of the halocline.…”

The Arctic Subpolar Gyre sTate Estimate: Description and Assessment of a Data‐Constrained, Dynamically Consistent Ocean‐Sea Ice Estimate for 2002–2017

“…Arctic Circumpolar Current: In the Laptev Sea it is thought that the circumpolar circulation of AW splits at ∼145 • E, with a fraction returning to Fram Strait along the Lomonosov Ridge (Rudels, 2015) and the remainder continuing along the basin's rim into the Western Arctic, although the exact partitioning is not well constrained. In the Western Arctic it is typically assumed that the AW continues to circulate cyclonically along the basin boundary, although both ASTE R1 (Grabon, 2020) and a modeling effort informed by observed radionuclide distributions (Karcher et al, 2012) suggest a weak anticyclonic circulation during the last decade. Recent work analyzing all available current meters (updated from Baumann et al (2018)) has yielded velocity probability distributions for the Arctic region.…”

“…All rights reserved. data comparisons (e.g., Grabon, 2020), the interpolation introduces additional information that was not strictly solved for by the model. An alternate approach is to vary the salinity bounds to gauge the sensitivity of the heat content within this watermass to the vertical discretization in the model.…”

“…For more accurate estimation of halocline-integrated quantities one approach is to "interpolate" the salinity in the vertical to a finer grid to find the exact depths at which salinity fits within the given bounds. Though this is often done during model-data comparisons (e.g., Grabon, 2020), the interpolation introduces additional information that was not strictly solved for by the model. An alternate approach is to vary the salinity bounds to gauge the sensitivity of the heat content within this watermass to the vertical discretization in the model.…”

The Arctic Subpolar gyre sTate Estimate (ASTE): Description and assessment of a data-constrained, dynamically consistent ocean-sea ice estimate for 2002-2017

“…In the Laptev Sea it is thought that the circumpolar circulation of AW splits at ∼145°E, with a fraction returning to Fram Strait along the Lomonosov Ridge (Rudels, 2015) and the remainder continuing along the basin's rim into the Western Arctic, although the exact partitioning is not well constrained. In the Western Arctic it is typically assumed that the AW continues to circulate cyclonically along the basin boundary, although both ASTE_R1 (Grabon, 2020) and a modeling effort informed by observed radionuclide distributions (Karcher et al, 2012) suggest a weak anticyclonic circulation during the last decade. Recent work analyzing all available current meters (updated from Baumann et al, 2018) has yielded velocity probability distributions for the Arctic region.…”