Internal variability of Arctic liquid freshwater content in a coupled climate model large ensemble

Liquid freshwater content (LFWC) within the Arctic Ocean has rapidly accumulated over the recent historical period as multiple sources of freshwater have intensified in the warming polar climate. Many of the physical processes surrounding freshwater variability, including the influence of anthropogenically-driven warming, are still not fully understood. Using 22 realizations of the CMIP6 model EC-Earth3 with identical radiative forcing, we utilize a spatial pattern matching technique to separate the internal and forced spatiotemporal patterns in LFWC and reconstruct historical trends. We find that quantifying internal variability and external forcing patterns hinges on an accurate oceanic reanalysis to represent the historical trend. With SODA3.3.2, internal variability arising from spatiotemporal sea surface height patterns accounts for 64.5% of the total LFWC historical trend, and reconstruct an observed trend of + 0.86 m per decade. In ORAS5, the internal variability pattern accounts for 94.3% of the spatiotemporal pattern, but produces an incongruent reconstruction of historical LFWC trends. These results thus highlight the need for more in-situ observations to inform reanalysis and modeling efforts. Across oceanic reanalyses, we find that internal variability arising from the Arctic Oscillation may represent a low-end estimate of internal variability influence on LFWC, whereas sea surface height more accurately discerns long-term spatiotemporal trends.