Water Mass Transformation in the Greenland Sea during the Period 1986–2016

Abstract

Hydrographic measurements from ships, autonomous profiling floats, and instrumented seals over the period 1986–2016 are used to examine the temporal variability in open-ocean convection in the Greenland Sea during winter. This process replenishes the deep ocean with oxygen and is central to maintaining its thermohaline properties. The deepest and densest mixed layers in the Greenland Sea were located within its cyclonic gyre and exhibited large interannual variability. Beginning in winter 1994, a transition to deeper (>500 m) mixed layers took place. This resulted in the formation of a new, less dense class of intermediate water that has since become the main product of convection in the Greenland Sea. In the preceding winters, convection was limited to <300-m depth, despite strong atmospheric forcing. Sensitivity studies, performed with a one-dimensional mixed layer model, suggest that the deeper convection was primarily the result of reduced water-column stability. While anomalously fresh conditions that increased the stability of the upper part of the water column had previously inhibited convection, the transition to deeper mixed layers was associated with increased near-surface salinities. Our analysis further suggests that the volume of the new class of intermediate water has expanded in line with generally increased depths of convection over the past 10–15 years. The mean export of this water mass from the Greenland Sea gyre from 1994 to present was estimated to be 0.9 ± 0.7 Sv (1 Sv ≡ 106 m3 s−1), although rates in excess of 1.5 Sv occurred in summers following winters with deep convection.

Natural drivers of multidecadal Arctic sea ice variability over the last millennium

“…2a). Within this interval, similar to the situation at the present day, we propose that the boundary between the cool and moderately saline high δ 18 O eqil. convectively-mixed waters and the warm and saline low δ 18 O eqil.…”

Sea ice volume variability and water temperature in the Greenland Sea

“…The Greenland Sea is a key region of deep ocean convection (Marshall and Schott, 1999;Brakstad et al, 2019) and an inherent part of the Atlantic Meridional Overturning Circulation (AMOC) (Rhein et al, 2015;Buckley and Marshall, 2016). The intensity of convection is governed by buoyancy (heat and freshwater) fluxes at the ocean-atmosphere boundary, as well as oceanic buoyancy advection into the region.…”

The Contrasting Dynamics of the Buoyancy-Forced Lofoten and Greenland Basins

“…Furthermore, our conceptual model focuses on the role of temperature regarding atmospheric forcing and ocean dynamics. Salinity variations (or freshwater fluxes) can play an important role for, for example, the strength of the density gradient between the Lofoten and Greenland Basins, the dense water formation in the interior (e.g., Rossby et al 2009;Brakstad et al 2019), the atmospheric buoyancy forcing and slope current dynamics due to river runoff (Lambert et al 2018). Spall (2012) has investigated the role of precipitation in a onebasin marginal sea and shows that abrupt transitions are possible due to a shutdown of convection.…”

“…Both mechanisms tend to reduce convection events by stabilizing the water column. However, in recent years, mixed layer depths in the Greenland Basin have deepened, possibly associated with increased near-surface salinities (Brakstad et al 2019). Due to the rather complex nature of the Nordic seas it is therefore difficult to predict how it will respond to climate change and which physical mechanisms drive its response.…”