Meltwater Lenses Over the Chukchi and the Beaufort Seas During Summer 2019: From In Situ to Synoptic View

Abstract

The Arctic Ocean surface salinity is largely influenced by river discharges and sea ice melting. As in any cold environment, salinity largely determines the seawater density structure which, in turn, controls the ocean dynamics and vertical mixing. In the Arctic Ocean, Pacific Water (PW), which enters through the Bering Strait to the Chukchi Sea, is one of the primary low salinity sources. Over the Chukchi Shelf, two distinct Pacific-originated water masses are commonly observed: the relatively salty Bering Sea Water (BSW; between 32 and 33 practical scale salinity (pss)) and the relatively fresh Alaskan Coastal Water (ACW; between 31 and 32 pss;Coachman et al., 1975;Steele et al., 2004). ACW is mainly composed of Riverine Water (RW), with a strong contribution from the Yukon River. ACW and the easternmost branch of BSW are injected into the Beaufort Gyre trough Barrow Canyon, while the westernmost branch is advected northward and carries PW toward the Transpolar Drift (Timmermans et al., 2014).

Sea Ice Meltwater in the Beaufort Gyre: A Comprehensive Analysis Using Sea Surface Salinity Data from SMOS

“…A possible explanation of such a good fitting between both variables (R 2 = 0.96) is that the observed sea surface is smaller and southern when sea ice cover expands, leaving only the saltier surface waters of the Norwegian and Barents Seas to be measurable from SMOS. On the other hand, a larger ocean surface is measurable when sea ice retreats, and the fresher SSS retrieved could reveal the potential capability of SMOS in detecting the sea ice melt footprint, as it has been recently reported in Supply et al (2022). and 3a).…”

“…For each grid cell to be considered as part of a MWL, we applied two criteria: 1) the number of days covered by sea ice (SIC > 10%) must range between 2 to 29 days, i.e. during September at least two days have been ice covered; and 2) monthly mean values of SSS must be less or equal than 25 psu to ensure the presence of sea-ice meltwaters (Supply et al, 2022). Once the MWLs were delimited, we calculated their area, seawater properties, and the volume of freshwater released from sea ice melting (see Section 3.3).…”

“…Recent research has pointed out the important role that sea ice transport exerts in redistributing freshwater into and out of the BG (Cornish et al, 2023). The ocean surface freshening induced by sea ice melting has been shown to restrict the momentum transfer from the atmosphere to the ocean, thereby enhancing near-surface stratification of the upper ocean (Supply et al, 2022). However, the impact of sea ice retreat on freshwater dynamics and the broader climate system remains poorly constrained, being an active area of current scientific research.…”

“…In recent decades satellite data, in situ observations, and model reanalysis outputs have been integrated not only for FWC estimations (e.g. Fournier et al (2020); Solomon et al (2021); Umbert et al (2023)) but also for improved analysis of sea ice decline and river discharge impact on the Arctic Ocean (Kilic et al, 2018), as well as in detecting a punctual meltwater lens (MWL) induced by sea ice melting (Supply et al, 2022).…”

Significant Diurnal Warming Events Observed by Saildrone at High Latitudes

“…In contrast to the effect of melting sea ice, precipitation should decrease the salinity of a much thinner layer at the ocean surface, trapping heat into the layer and resulting in a shallow warming penetration depth, such as shown in Figure 7b. The freshwater generated by sea ice melt could accumulate in the upper tens of meters of the ocean (Peralta‐Ferriz & Woodgate, 2015; Supply et al., 2022), much thicker than the warm layer thickness of a few meters. Thus, we infer the thermal structure tends to be unstable due to the small difference in density between stratified layers caused by a small vertical gradient of salinity.…”