Temporal and spatial distribution of dimethylsulfide in the subarctic northeast Pacific Ocean: a high-nutrient–low-chlorophyll region

Abstract

Dimethylsulfide (DMS) was measured in the upper 400 m of the northeast Pacific from February 1996 to June 2001. The sampling took place along Line P (48 • 34.5 N, 125 • 30 W to 50 • N, 145 • W). DMS concentrations increased diurnally from a pre-dawn low to a midday maximum and from coastal waters to open ocean, in a high-nutrient-low-chlorophyll-a (HNLC) water mass. The mean surface DMS in winter was 2 nM, in spring 6 nM and in summer 10 nM. Our June surface DMS amounts were comparable with those obtained by the Pacific Marine Environmental Laboratory. A sea to air flux of DMS at Station P (50 • N, 145 • W) was high in the summer of 1997 and the early autumn of 1998 and 2000 and was significantly higher than at other Line P stations. The average flux along Line P was 27 µmol m −2 d −1 by Wanninkhof's formula while that by Liss and Merlivat was 16 µmol m −2 d −1. DMS profiles showed a decreasing trend with depth, as did temperature and chlorophyll-a (Chl-a), but an increasing trend with salinity and nitrate. Average DMS concentrations at mixed-layer depth (DMS MLD) were low in winter at an average of 2.4 nM, moderate in spring at 8 nM and high in summer at 16 nM. For open ocean stations P20 and P26 DMS MLD was high, while Chl-a MLD was low for late spring and early summer during 1996-1998. That is the "summer paradox" phenomenon. The ratio of DMS MLD to Chl-a MLD was out of phase with the mixed-layer depth. Our data confirm the high DMS concentrations previously reported for this region and suggest that this is characteristic of the subarctic HNLC region.