Depth profiles of suspended carbon and nitrogen along a North Pacific transect: Concentrations, isotopes, and ratios

Abstract

We present concentrations of total particulate carbon (PC), carbonate (PIC), total particulate nitrogen (PN), δ¹³C and δ¹⁵N of suspended particles along a North Pacific transect. In the upper 400 m, suspended PIC to particulate organic carbon (POC) ratios generally follow published sinking PIC/POC ratios. Below 600 m, suspended PIC/POC become significantly lower than sinking PIC/POC, likely indicating PIC dissolution within the suspended load. In three out of the five stations, suspended PN δ¹⁵N increase with depth from the euphotic zone to the thermocline, consistent with previous observations in many ocean regions (e.g.,BATS and HOT). However, in the other two stations where phytoplankton blooms were encountered, high suspended PN δ¹⁵N (up to 12‰) were observed in the euphotic zone, which was likely caused by the export of low-δ¹⁵N PN during the phytoplankton blooms. Average C_(org) : N ratio of suspended particles along the transect is 5.1 ± 0.2, with the value in the subtropical gyre (5.8 ± 0.3) slightly higher than the subarctic gyre (4.6 ± 0.2).