Arctic Ocean and Hudson Bay Freshwater Exports: New Estimates from Seven Decades of Hydrographic Surveys on the Labrador Shelf

Abstract

While reasonable knowledge of multi-decadal Arctic freshwater storage variability exists, we have little knowledge of Arctic freshwater exports on similar timescales. A hydrographic time series from the Labrador Shelf, spanning seven decades at annual resolution, is here used to quantify Arctic Ocean freshwater export variability west of Greenland. Output from a high-resolution coupled ice-ocean model is used to establish the representativeness of those hydrographic sections. Clear annual to decadal variability emerges, with high freshwater transports during the 1950s and 1970s–80s, and low transports in the 1960s, and from the mid-1990s to 2016, with typical amplitudes of 30 mSv (1 Sv = 106 m3 s-1). The variability in both the transports and cumulative volumes correlates well both with Arctic and North Atlantic freshwater storage changes on the same timescale. We refer to the "inshore branch" of the Labrador Current as the Labrador Coastal Current, because it is a dynamically- and geographically-distinct feature. It originates as the Hudson Bay outflow, and preserves variability from river runoff into the Hudson Bay catchment. We find a need for parallel, long-term freshwater transport measurements from Fram and Davis Straits, to better understand Arctic freshwater export control mechanisms and partitioning of variability between routes west and east of Greenland, and a need for better knowledge and understanding of year-round (solid and liquid) freshwater fluxes on the Labrador shelf. Our results have implications for wider, coherent atmospheric control on freshwater fluxes and content across the Arctic and northern North Atlantic Oceans.

Dominant Terms in the Freshwater and Heat Budgets of the Subpolar North Atlantic Ocean and Nordic Seas From 1992 to 2015

“…Evidence suggests that over multidecadal time scales, Arctic freshwater flux and LFWC in the SPNA are tightly linked (Karcher et al, 2005; Koenigk et al, 2007; Peterson et al, 2006). This linkage has been underscored by a recently published study of freshwater flux along the Labrador Current (Florindo‐López et al, 2020). Contrary to our shorter, 24‐year analysis using ECCOv4, Florindo‐López et al (2020) demonstrated a high correlation between Arctic flux and LFWC in the SPNA.…”

“…This linkage has been underscored by a recently published study of freshwater flux along the Labrador Current (Florindo‐López et al, 2020). Contrary to our shorter, 24‐year analysis using ECCOv4, Florindo‐López et al (2020) demonstrated a high correlation between Arctic flux and LFWC in the SPNA. The high level of detail in their analysis, afforded by a high‐resolution model (∼5 km in the Labrador Sea) together with a long observational record (70 years) across the Labrador Shelf, enabled a better representation of the Labrador Current System, including a distinct coastal branch known as the Labrador Coastal Current.…”

Freshwater in the Arctic Ocean 2010–2019

“…The isotopically lighter meteoric fractions are used to quantify freshwater that originates from the atmosphere (directly or indirectly), and the isotopically heavier fractions similarly quantify the signal of brine rejected from sea ice and thereby the amount of ice formed from that seawater. The Forryan et al (2019) study shows that, within uncertainties, the geochemical approach produces the same surface freshwater flux as the budget approach.…”

“…An exactly equivalent interpretation is that surface freshwater fluxes and the relatively fresh Bering Strait sea water inflow combine to dilute the relatively saline Atlantic water inflow, which then become the outflows (allowing for storage), where "relatively" means relative to the boundary mean salinity. Forryan et al (2019) pursue the surface freshwater flux approach, noting that (as is well known, e.g., Östlund and Hut, 1984) evaporation and freezing are distillation processes that leave behind a geochemical imprint via oxygen isotope anomalies on the affected freshwater in the sea ice and seawater. In the case of evaporation, distillation (here, isotopic fractionation) preferentially removes lighter oxygen isotopes from seawater, leaving behind in the seawater a proportion of heavier isotopes.…”

A climate index for the Newfoundland and Labrador shelf

“…Sea ice season duration and maximum cover area are estimated from ice cover products obtained from the Canadian Ice Service (CIS). The methodology is described in Galbraith et al (2020) and briefly summarized here. The source CIS products consist of weekly geographic information system (GIS) charts covering the east coast for the period 1969-2020 and Hudson Bay for the period 1980-2020.…”