Small-Scale Features in the ΔfCO2 Distributions Along the TN413 Cruise Track in the North Pacific Subtropical Gyre and Equatorial Pacific

Abstract

Rising atmospheric CO2 levels are contributing to widespread changes in the global ocean carbon budget. Long-term trends on the air-sea flux of CO2 have demonstrated that the North Pacific Subtropical Gyre (NPSTG) is a net sink of CO2, whereas the equator is a net source. There are sparse smaller spatial and temporal scale analyses of ΔfCO2 features in the Pacific Ocean; this study aimed to resolve this by collecting underway fCO2, SSS, SST, and phytoplankton abundance data from cruise TN413 from February 24—March 12, 2023. It was hypothesized that ΔfCO2 levels would be similar to previous data—lower in the gyre and higher in the equatorial region. In addition, horizontal gradients in ΔfCO2 in the NPSTG would be a result of biological processes rather than physical because of its highly stratified water. ΔfCO2 features in the equatorial Pacific would be driven by physical processes due to upwelling bringing old, CO2-supersaturated water to the surface. Current ΔfCO2 data matched previous data from March 2000, however there were two areas in the NPSTG where significant horizontal gradients were present (6°N and 10°N). Because of the anticorrelation between ΔfCO2 and SST at 6°N, upwelling is thought to have transported nutrients, influencing primary productivity, and decreasing fCO2 by photosynthesis. The gradient at 10°N had positive correlations with SSS and SST, so it was probably caused by equatorial water that was transported by a tropical instability wave or an eddy. Further research is needed to confidently identify the source of the feature at 10°N.