The Particulate Organic Carbon-to-Nitrogen Ratio Varies With Ocean Currents

Linlin Zhang,Yuhao Teng,Shengjun Xiao,Wen Luo,Tao Huang

doi:10.3389/fenvs.2021.757471

Abstract

Ocean currents could adjust ocean carbon and nitrogen composition which are an important part of the global carbon and nitrogen cycle. We procured global concentrations of particulate carbon and nitrogen in different depths, classified them according to ocean currents (upper 300 m), and analyzed POC-to-PON ratio (particulate organic carbon-to-nitrogen ratio) variations. We found that the regions with currents have a higher ratio than those without currents in the northern hemisphere, except in 50°–60°N (median ratio without currents is 8.38). Warm currents (median ratio ranges from 5.96 to 8.44) have a higher ratio than cold currents (6.19–8.89), except for the East Greenland Current (reach to 8.44) and Labrador Current (reach to 8.89). Meanwhile, we also analyzed the effects of ocean currents’ flowing and found that the distributions of the POC-to-PON ratio vary in different current types (e.g., cause of formation and distance from the shore). Generally speaking, the POC-to-PON ratio of the eolian currents and near-ocean currents change fiercer than that of compensation currents and near-coast currents. Ocean currents also have a buffering effect in the variation between surface and deep water, which prevents the severe change of the POC-to-PON ratio. The high-value anomaly of POC-to-PON caused by the confluence of warm and cold currents was also analyzed. It can be deduced that the high ratio in the high-latitude region was mainly caused by the terrigenous organic matter (especially carbon) and low nitrogen.

Highlights

As an important part of the global biogeochemistry cycle, the ocean carbon and nitrogen cycle has always been concerned
We procured global particulate organic carbon and nitrogen of phytoplankton in oceans, analyzed the POC-to-PON ratio of the global variations of surface water and the median ratio based on ocean currents
We found that the global ocean median ratio, especially in the southern hemisphere, is close to the Redfield ratio, whereas the ratio is a little higher in the northern hemisphere, it even reaches 8.63 in 80°N–90°N

Summary

INTRODUCTION

As an important part of the global biogeochemistry cycle, the ocean carbon and nitrogen cycle has always been concerned. Many studies have been conducted on variations in particulate carbon, nitrogen, and the phosphorus ratio of oceans, lakes, rivers, and estuaries. In order to study ocean currents’ influence on the POC-to-PON ratio, all data have been classified according to ocean currents (Orsi et al, 1995; Bischof et al, 2004a; Gyory et al, 2004a; Bonhoure et al, 2004; Rowe et al, 2004; Pidwirny, 2006). Because the amount of data is huge and the data are not evenly distributed in space and time, the histogram and quantile analysis methods are used to analyze the variation in the POC-to-PON ratio from a statistical point of view. The given POCto-PON ratio data can be divided into several categories according to the ocean current type or flow direction, and the histogram analysis is performed with every category. Boxplot results reflect the upper and lower boundaries, upper quartile, lower quartile, and the median of the data set

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DATA AVAILABILITY STATEMENT