Wintertime Water Mass Transformation in the Western Iceland and Greenland Seas

Abstract

Hydrographic and velocity data from a 2018 winter survey of the western Iceland and Greenland Seas are used to investigate the ventilation of overflow water feeding Denmark Strait. We focus on the two general classes of overflow water: warm, saline Atlantic‐origin Overflow Water (AtOW) and cold, fresh Arctic‐origin Overflow Water (ArOW). The former is found predominantly within the East Greenland Current (EGC), while the latter resides in the interior of the Iceland and Greenland Seas. Progressing north to south, the properties of AtOW in the EGC are modified diapycnally during the winter, in contrast to summer when along‐isopycnal mixing dominates. The water column response to a 10‐days cold‐air outbreak was documented using repeat observations. During the event, the northerly winds pushed the freshwater cap of the EGC onshore, and convection modified the water at the seaward edge of the current. Lateral transfer of heat and salt from the core of AtOW in the EGC appears to have influenced some of this water mass transformation. The long‐term evolution of the mixed layers in the interior was investigated using a 1‐D mixing model. This suggests that, under strong atmospheric forcing, the densest component of ArOW can be ventilated in this region. Numerous anti‐cyclonic eddies spawned from the EGC were observed during the winter survey, revealing that these features can play differing roles in modifying/prohibiting the open‐ocean convection.

Role of air-sea heat flux on the transformation of Atlantic Water encircling the Nordic Seas

“…2c is likely biased by the large number of summertime hydrographic profiles; also, the re-ventilation process is a relatively new phenomenon. Furthermore, recent studies have demonstrated the importance of lateral processes on the water mass transformation in the EGC 13 , 14 . For example, the ocean response to a cold-air outbreak measured by a joint aircraft-ship campaign in winter 2018 was moderated by lateral advection and mixing near the EGC 14 .…”

“…These latter two currents contribute to the overturning in the high Arctic and also play a fundamental role in the recently documented Arctic Atlantification 37 , 38 . Recent studies have demonstrated that the AW in the EGC, as well as that in the boundary current north of Svalbard in the Amundsen Basin, can be further transformed as a result of reduced ice cover in these regions 13 , 17 , 39 . Hence, it remains unclear how much the reduction in air–sea cooling along the NwAFC might be compensated for by the re-ventilation along the EGC.…”

Coupled atmosphere–ocean observations of a cold‐air outbreak and its impact on the Iceland Sea

“…Furthermore, our observations indicate that, in the interior regime, surface cooling dominated the response with less influence from lateral effects. (We note that isolated eddies shed from the boundary current can modulate the ML response in the interior Iceland and Greenland Seas, as demonstrated by Huang et al ., 2021. )…”

“…(1986). It has previously been successfully used to simulate changes in ML properties in the western Nordic Seas (e.g., Moore et al ., 2015; Våge et al ., 2018; Brakstad et al ., 2019; Huang et al ., 2021). Here we use CTD profiles from the base of both survey triangles during the pre‐ and early‐CAO period as initial conditions, and apply atmospheric forcing from ERA5.…”

“…Some of these patches reflect changes in the distribution of sea ice and associated colder surface waters, but some appear to reflect other processes such as the upward mixing of warmer subsurface Atlantic‐origin waters, or lateral advection from eddies. Numerous eddies were observed in the hydrographic data (Huang et al ., 2021) and these are known to be an important vehicle for heat transport in such marginal seas (Spall, 2011).…”