Understanding Differences in North Atlantic Poleward Ocean Heat Transport and Its Variability in Global Climate Models

Erica Madonna,Anne Britt Sandø

doi:10.1029/2021gl096683

Abstract

AbstractThe ocean heat transport from the North Atlantic to the Barents Sea impacts the sea ice extent and the energy budget of the Arctic. The analyzed climate models from the fifth (CMIP5) and sixth (CMIP6) phases of the Coupled Model Intercomparison Project show large intermodel differences in the ocean heat transport with biases of several Terawatts at the Iceland‐Scotland Ridge and Barents Sea Opening (BSO). While both model generations show a large spread in mean volume transports, in CMIP6 temperatures are more homogeneous and realistic, yielding heat transports closer to observations. On all time scales, changes in heat transport reflect changes in volume transport, while temperature changes affect the heat transport variability on longer time scales, especially at the BSO. The temporal variability of heat and volume transports is linked to wind forcing south of Iceland and along the Norwegian coast in all models but has different magnitudes.

Highlights

Ocean currents are key components of the climate system, as they transport energy poleward from the tropics to high-latitudes
We focus on the Iceland-Scotland Ridge (ISR) and Barents Sea Opening (BSO) only, on the one hand, because the Fram Strait transports are strongly influenced by eddy-driven variability (Muilwijk et al, 2018), which cannot be realistically reproduced in the low-resolution global models
The co-variability on decadal time scales between OHT at the ISR and BSO is for most models positive

Summary

Introduction

Ocean currents are key components of the climate system, as they transport energy poleward from the tropics to high-latitudes. The poleward energy transport may be altered by anthropogenic climate change (Burgard & Notz, 2017; Huang et al, 2017; Nummelin et al, 2017; Spielhagen et al, 2011), leading to profound impacts on the fragile Arctic system, such as changes in the sea ice cover, the distribution of species, and economic activities (ACIA, Arctic Climate Impact Assessment, 2004). Trends in sea ice cover from most models that contributed to the Coupled Model Intercomparison Project Phase 5 (CMIP5) are less negative than the observed trends (Li et al, 2017; Stroeve et al, 2012). A distinct improvement in the representation of the sea ice volume and extent is obtained in Coupled Model Intercomparison Project phase 6 (CMIP6) (Davy & Outten, 2020; Notz and SIMIP Community, 2020), but numerous model biases persist, including too cold conditions in winter

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