Abstract
AbstractVariation in upper-ocean heat content is a critical factor in understanding global climate variability. Using temperature anomaly budgets in a two-decade-long physically consistent ocean state estimate (ECCOv4r3; 1992â2015), we describe the balance between atmospheric forcing and ocean transport mechanisms for different depth horizons and at varying temporal and spatial resolutions. Advection dominates in the tropics, while forcing is most relevant at higher latitudes and in parts of the subtropics, but the balance of dominant processes changes when integrating over greater depths and considering longer time scales. While forcing is shown to increase with coarser resolution, overall the heat budget balance between it and advection is remarkably insensitive to spatial scale. A novel perspective on global ocean heat content variability was made possible by combining unsupervised classification with a measure of temporal variability in heat budget terms to identify coherent dynamical regimes with similar underlying mechanisms, which are consistent with prior research. The vast majority of the ocean includes significant contributions by both forcing and advection. However advection-driven regions were identified that coincide with strong currents, such as western boundary currents, the Antarctic Circumpolar Current, and the tropics, while forcing-driven regions were defined by shallower wintertime mixed layers and weak velocity fields. This identification of comprehensive dynamical regimes and the sensitivity of the ocean heat budget analysis to exact resolution (for different depth horizons and at varying temporal and spatial resolutions) should provide a useful orientation for future studies of ocean heat content variability in specific ocean regions.
Highlights
Earthâs oceans play a critical role in regulating the global climate system (Bigg et al 2003; von Schuckmann et al 2016) and have been shown to act as a critical sink of excess atmospheric and land-based heat resulting from greenhouse gases (e.g., Barnett et al 2001, 2005; Pierce et al 2012; Trenberth et al 2014)
Advection-driven regions coincide with strong currents such as western boundary currents, the Antarctic Circumpolar Current and the tropics, while regions with a strong forcing signal are defined by shallower wintertime mixed layers and weak velocity fields
This study investigated the contribution of individual mechanisms to ocean heat content (OHC) variability at a range 541 of spatial and temporal scales
Summary
Earthâs oceans play a critical role in regulating the global climate system (Bigg et al 2003; von Schuckmann et al 2016) and have been shown to act as a critical sink of excess atmospheric and land-based heat resulting from greenhouse gases (e.g., Barnett et al 2001, 2005; Pierce et al 2012; Trenberth et al 2014). We take great care to examine the sensitivity of our results to spatial and temporal scales, in order to determine which patterns are most robust across scales With this analysis, a key question we hope to answer is under what circumstances is OHC variability primarily driven by atmospheric variability vs internal mechanisms? The sensitivity to temporal and/or spatial scale has been either focused on particular ocean regions, such as the North Atlantic (Buckley et al 2014, 2015), or on the global scale for the sea surface using observation-based analyses (Bishop et al 2017; Small et al 2019) and subsurface OHC variability based on climate models (Small et al 2020). The studyâs findings are further discussed in Section 6, with concluding remarks and suggestions for future work
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