DMS Transport from the West Indian Ocean to the Stratosphere during Asian Monsoon 2000-2016

Tuesday, 20 March 2018: 11:45
Salon Vilaflor (Hotel Botanico)
Kirstin Krüger1, Alina Fiehn2, Alexander Zavarsky3, Dennis Booge3, Elliot L Atlas4, Christa A Marandino5 and Birgit Quack3, (1)University of Oslo, Oslo, Norway, (2)University of Oslo, Geosciences Department, Oslo, Norway, (3)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (4)RSMAS, Miami, FL, United States, (5)GEOMAR, Kiel, Germany
Abstract:
Sulfur-containing compounds, such as dimethyl sulfide (DMS), are supersaturated in the surface ocean, which results in their emission to the atmosphere. DMS emissions above convectively active atmospheric regions such as the tropical West Pacific can reach the stratosphere (Marandino et al., 2013), where they impact the aerosol layer and climate.

During the OASIS research cruise on RV Sonne in the subtropical and tropical West Indian Ocean (WIO) in July and August 2014 (Krüger et al., 2015), oceanic concentrations and atmospheric mixing ratios of DMS were measured and first direct fluxes were successfully carried out using the eddy-covariance technique. The coastal upwelling southeast of Madagascar and the open ocean upwelling of the Chagos-Seychelles thermocline ridge were identified as biologically productive regions with enhanced DMS production and emissions. Eddy-covariance observed DMS emissions confirmed that the WIO is a hot spot region during boreal summer despite the emissions being lower than in the climatology from Lana et al. (2011).

Following, we calculated the seasonal and interannual variability of DMS transport from the WIO surface to the stratosphere for 2000-2016 with the Lagrangian transport model FLEXPART using ERA-Interim meteorological fields. We investigate the atmospheric transport relevant for DMS using a tropospheric lifetime of 1 day. The stratospheric entrainment of DMS tracer from the WIO shows a distinct annual cycle associated with the Asian monsoon. Over the 16 year time series, a slight increase in entrainment from the WIO to the stratosphere is found during all seasons. The interannual variability shows a relationship with sea surface temperatures in the WIO as well as the El Niño–Southern Oscillation. Positive sea surface temperature anomalies over the WIO and East Pacific lead to enhanced vertical uplift above the WIO. Finally, the role of the Indian Ocean in DMS delivery to the stratospheric aerosol layer is discussed.

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