Quantifying Velocity, Chlorophyll, Temperature, and Nutrients Relationships with Primary Productivity in the Western Equatorial Pacific

Abstract

Net primary productivity (NPP) and gross primary productivity (GPP) is a major component of the carbon cycle. NPP is defined as the amount of carbon biomass produced by primary producers over a given period of time and area. GPP is the combination of NPP and respiration. The NPP exceeds 100 billion tons of carbon per year on Earth and half of it comes from the ocean through phytoplankton. The equatorial Pacific Ocean is the largest tropical ocean on Earth and subsequently the largest oceanic source of CO2 to the atmosphere. Despite its importance, NPP in the west equatorial Pacific is poorly characterized due to the lack of data. Previous research suggests that strong upwelling is associated with increased nutrient concentration in the euphotic zone leading to an increase in primary productivity. However, the western equatorial Pacific is known for weaker upwellings compared to the eastern and central equatorial Pacific. This study was conducted aboard the R/V Thomas G. Thompson from December 28, 2023, to January 12, 2024, with the goal of identifying and quantifying the critical variables that have a substantial impact on NPP in the region including temperature, chlorophyll, dissolved nutrients, and current velocity. NPP and GPP was measured using in-situ oxygen incubations. The mean GPP found in this study range from −163.82 to 26.05 mmol O2 m−2 d−1. A combination of temperature, chlorophyll, dissolved nutrients, and current velocity can explain for 54.18% of the variance in GPP. There is a missing 45.82% not accounted for that requires further studies on factors that influence GPP such as iron, which is a limiting nutrient.