Distribution and cycling of dimethylsulfide, dimethylsulfoniopropionate, and dimethylsulfoxide during spring and early summer in the Southern Ocean south of New Zealand

Abstract.

Concentrations of total dimethylsulfoniopropionate (DMSPt) and its degradation products, dissolved dimethylsulfide (DMS) and dimethylsulfoxide (DMSOd), were measured in surface waters along three transects between 49 to 76°S latitude (November 2003 & 2005 and December 2004) in the New Zealand sector of the Southern Ocean. Most water samples were collected from the ship’s underway pump system, and concentrations of DMSPt, DMS and DMSOd obtained with this method showed excellent agreement with Niskin bottle-collected samples. Dissolved DMSP (DMSPd), on the other hand, was significantly higher in pump samples. Biological consumption rates for DMSPd and DMS were also measured in Niskin-collected surface waters at selected stations. Concentrations of DMSPt (12 to 52 nM) and DMS (0.6 to 3.2 nM) were moderate in open waters north of the seasonal sea ice (north of 63°S), and very low (< 12 nM DMSPt and < 1 nM DMS) where sea ice coverage was >80% (65 – 73°S; November transects). High concentrations of DMSPt (up to 95 nM) and DMS (up to 30 nM), and high DMS:DMSPt ratios, were observed on the northern boundaries of the seasonal sea ice (63 to 68°S) and in the northern Ross Sea (74 – 76°S). Surface water DMSOd concentrations were variable (1 – 55 nM), but generally higher in ice melt zones and the northern Ross Sea, especially in summer (December 2004). Rates of biological DMS and DMSPd consumption were elevated in ice melt zones, but were generally quite low (<1 nMDMSd⁻¹ and<2.5nMDMSPd d⁻¹), except in the Ross Sea polynya where consumption rates reached 7 nM DMS d⁻¹ and 13 nM DMSPd d⁻¹. This data set provides much needed information regarding the distribution and cycling of DMSP, DMS and DMSO in a poorly studied area of the Southern Ocean. Our findings show that areas of ice melt and the northern Ross Sea are zones of elevated DMS concentrations and sea-air fluxes and also rapid cycling of DMSP and DMS.