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

Abstract

The Arctic region has experienced large changes in recent decades. These include near-surface air temperature warming at twice the global rate (Richter-Menge & Jeffries, 2011), rapid decline in multi-year sea ice (Kwok & Cunningham, 2015), enhanced solar radiation absorption in the Western Arctic upper ocean (Timmermans et al., 2018), increased river and glacial discharge (Bamber et al., 2012(Bamber et al., , 2018Proshutinsky et al., 2020), and increased influxes of freshwater from the Pacific (Woodgate, 2018) and heat from the Atlantic (Polyakov et al., 2011). Many of these changes have been suggested to trigger positive feedbacks.

Arctic and Sub‐Arctic Mechanisms Explaining Observed Increasing Northward Flow Through the Bering Strait and Why Models May Be Getting It Wrong

“…We note that Nguyen et al. (2012), which reproduced the Bering Strait flow well, also well‐matched Bering Strait salinities, whereas ASTE (Nguyen, Pillar, Ocaña, Bigdeli, et al., 2021), which does not obtain the increasing flow trend, has Bering Strait salinities (Nguyen, Pillar, Ocaña, Smith, & Heimbach, 2021) ∼0.6 psu higher than observations. By Equation , assuming DOT remains constant, that salinity change in the ESS would reduce the flow by ∼1.4 cm/s, equivalent to ∼7 years of the long‐term observational trend. Since wind‐driven lowering of OBP and DOT in the ESS is a dominant mechanism, model results may also be sensitive to inadequacies in wind‐water coupling in a region with seasonal sea ice.…”

“…Removing that entire input (assuming ESS salinities of ∼30 psu, area of 1,082 × 10 3 km 2 (Jakobsson et al., 2008), and mixing into a 50 m water column) is equivalent to a ∼0.1 psu salinization, only 5% of our 11‐year change of 1.87 psu. To achieve this salinization by brine rejection would require 2 m more ice formation in 2014 than in 2003, an almost 50% increase of the estimated existing seasonal cycle (∼4 m, Arctic Subpolar gyre sTate Estimate [ASTE] data (Nguyen, Pillar, Ocaña, Bigdeli, et al., 2021; Nguyen, Pillar, Ocaña, Smith, & Heimbach, 2021)) and note there are no significant trends in sea‐ice concentration in the region (Special Sensor Microwave Imager data, Figure 1j). Even generous estimates of upwelling (e.g., ∼34 psu water from ∼100 m depth) would need to fill ∼10% of the existing depth of the ESS, which seems unlikely.…”

“…Thus, models assimilating/tuned to these older satellite data sets will be missing a vital forcing of the strait flow. To our knowledge, this includes ASTE (Nguyen, Pillar, Ocaña, Bigdeli, et al., 2021; using JPL Mascon Release 5, version 2), but not Nguyen et al. (2012), which has a more accurate simulation of the Bering Strait flow. Since the Pacific Water is found to enter the ESS driving region, correct simulation of the salinity of the Bering Strait throughflow appears essential to maintain the correct forcing.…”

“…Thus, models assimilating/tuned to these older satellite data sets will be missing a vital forcing of the strait flow. To our knowledge, this includes ASTE (Nguyen, Pillar, Ocaña, Bigdeli, et al., 2021; using JPL Mascon Release 5, version 2), but not Nguyen et al. (2012), which has a more accurate simulation of the Bering Strait flow.…”

Relative Roles of Plume and Coastal Forcing on Exchange Flow Variability of a Glacial Fjord

“…Simulation initialization and boundary forcing is taken from the Arctic Subpolar Gyre State Estimate “ASTE” (Nguyen et al., 2021). Initial temperature, salinity and velocity fields were generated from a spin‐up simulation of 3 months in which the boundary forcing was held steady and no surface forcing was applied.…”