Abstract
The North Pacific Ocean is a significant carbon sink region, but little is known about the dynamics of particulate organic carbon (POC) and the influences of physical and biological processes in this region at the basin scale. Here, we analysed high-resolution surface POC data derived from MODIS-Aqua during 2003–2017, together with satellite-derived sea surface chlorophyll and temperature (SST). There are large spatial and temporal variations in surface POC in the North Pacific. Surface POC is much lower in the subtropical region (<50 mg m−3) than in the subarctic region (>100 mg m−3), primarily resulting from the south-to-north variability in biological production. Our analyses show significant seasonal and interannual variability in surface POC. In particular, there is one peak in winter-spring in the western subtropical region and two peaks in late spring and fall in the western subarctic region. Surface POC is positively correlated with chlorophyll (r = ~1) and negatively correlated with SST (r = ~−0.45, P < 0.001) south of 45°N, indicating the strong influence of physically driven biological activity on the temporal variability of POC in the subtropical region. There is a significantly positive but relatively lower correlation coefficient (0.6–0.8) between POC and chlorophyll and an overall non-significantly positive correlation between POC and SST north of 45°N, reflecting the reduction in the POC standing stock due to the fast sinking of large particles. The climate modes of the Pacific Decadal Oscillation, El Niño–Southern Oscillation and North Pacific Gyre Oscillation have large impacts on POC in various seasons in the subtropical region and weak influences in the subarctic region. Surface POC was anomalously high after 2013 (increased by ~15%) across the basin, which might be the result of complex interactions of physical and biological processes associated with an anomalous warming event (the Blob).
Highlights
The North Pacific Ocean undergoes strong temporal changes in physical processes, with implications for biogeochemistry
The POC level varies by a factor of two from the subtropical to the subarctic region, i.e., there are much higher values of POC in the subarctic region (>100 mg m−3) than in the subtropical region (
The POC:Chl ratio is lower in the subarctic region, which might be partly attributed to the decreased phytoplankton C:Chl ratio and rapid sinking of large-size particles
Summary
The North Pacific Ocean undergoes strong temporal changes in physical processes, with implications for biogeochemistry. Di Lorenzo et al.[16] reported that NPGO has played a dominant role in regulating surface salinity, nutrients and chlorophyll at the decadal timescale in the Northeast Pacific These findings imply that climate modes have impacts on the temporal variability of the surface POC in the North Pacific Ocean. Previous studies have indicated that there are large spatial and temporal variabilities in the surface POC of the North Pacific that are influenced by physical and biological processes. The objectives of this study are to evaluate the spatial and interannual variability of surface POC in the North Pacific, to analyse the different influences of physical and biological processes and to explore the impacts of major climate modes and the Blob on the dynamics of POC across the basin. The surface water in the NPSG is known as an “ocean desert” due to the conditions of strong stratification and severe nutrient depletion in the upper layer[29]
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