Recent Upper Arctic Ocean Warming Expedited by a Summertime Internal Atmospheric Process

Abstract:

The upper ocean heat content in the Arctic has risen significantly over the last few decades, which is primarily attributed to increased poleward atmospheric and oceanic heat transport and enhanced atmospheric heat entered the Arctic Ocean favored by anthropogenically driven reduction of the sea ice coverage. Here, using a variety of observational and modeling analyses, we demonstrate that a summertime internal atmospheric process, characterized by a large scale circulation trend toward a barotropic high pressure over the Arctic Ocean, could also play an important role in contributing to upper ocean (0 - 50m) warming in summer and fall in the past two decades. In contrast to the anthropogenic greenhouse effect and related positive feedbacks that induce oceanic warming throughout the year, the internal atmospheric process described in this study causes upper (0 - 50m) Arctic Ocean warming primarily through its dynamical impacts in adiabatically warming the air temperature in the Arctic and triggering sea ice-albedo feedback in the melt season. The dynamically warmed air temperature and reduced sea ice can jointly warm the upper ocean by enhancing the ocean’s absorption of longwave and shortwave radiation. A fingerprint analysis of large ensemble model simulations and a nudging experiment in which a model’s wind fields in the Arctic is constrained toward the observed state support this mechanism –warming due to internal variability could reach about 62% of that due to anthropogenic forcing in the past two decades. Given this ratio, around 38% of the observed warming trend from 2000 to 2018 in the upper Arctic Ocean in summer and fall could be attributable to the internal atmospheric process which represents an important source of the recent upper Arctic Ocean warming. Thus, a model’s capability in replicating this internal process determines its sensitivity and creditability in simulating oceanic response to climate forcing in the Arctic.