Climatic effect on DMS producers in the NE sub-Arctic Pacific: ENSO on the upper ocean

Abstract

We examined dimethylsulphide (DMS) data of two locations (P26 and P20) 1996–2001 in sub-Arctic NE Pacific with emphasis on 2 yr of DMS production measured in June and September of 1999 and 2000. At Station P26, integrated DMS to mixed layer depth (MLD) in June during 1999–2001 La Ni˜na period averaged 102 ± 25 μmol m-2 or only 42% of the average of 242 ± 27 μ mol m-2 measured during 1997–1998 El Ni˜no period. The summer integrated DMS to MLD of 246 μmol m-2 in the year 2000 was 61% of summer average in the period 1996–1998 of 402 ± 115 μmol m-2. At Station P20 where the mean DMS level of the MLD in June during the La Ni˜na years of 1999–2001 was 77 ± 7 μmol m-2, about 35% of 232 ± 22 μmol m-2 during the 1997–1998 El Ni˜no. Phytoplankton species rich in DMSP (an algal precursor to DMS) were also more abundant in 1998 than in the years 1999–2001 with low DMS. The ENSO event was characterized by warmer, more stratified waters with MLD shallowing to about 19 m from 1996 to early 1998, compared to the following years. These results provide a first example of how climate fluctuations, through altering the physical and chemical properties of the upper ocean, may influence the structure of the phytoplankton assemblage and hence DMS concentrations in the open ocean.