Outline of climate and oceanographic conditions in the Indian Ocean in the recent years: an update to August 2013

Outline of climate and oceanographic conditions in the Indian Ocean in the recent years: an update to August 2013

Year of publication 2013

Product type Meeting

Edition 1

Synopsis (short abstract) In this paper, we provide an update on the trends of climate and oceanographic conditions in the Indian Ocean and in sub-regions (Somali basin, East and West Equatorial areas, Mozambique Channel and Maldives). The ENSO cycle has been largely fluctuating between ENSO-neutral and Niña conditions during the past 4 years. Positive sea surface temperature (SST) anomalies have prevailed since the early 2000 over the West Indian Ocean (WIO). Substantial deepening of the thermocline occurs in the WIO in relation with intense El Niño events, but the opposite response (shoaling) during La Niña events is not clear on the long term. Since 2008, SOI has shown predomintly positive values (Niña) and thermocline has shoaled without major disruption along this trend until April 2011. Chlorophyll (SSC) has shown a declining trend over 2006-2010, followed by a slight increase from October 2010 to May 2011 in association with a Niña event, then continued to decline until March 2013. Then, the trend revers ed and positive anomalies developed from May 2013 onwards. Highly positive SSC anomalies were found in July-September 2013 in the Somali basin (40% above normal), suggesting an intensification of the Somali upwelling. In other areas, SSC was about the average in 2013 (Mozambique Channel, Maldives) or still slightly negative (10 % below normal) in the West equatorial (December 2012 to February 2013) and East equatorial areas. The overall chlorophyll- depleted conditions for 2006-2012 (except 2011 ) in the WIO, when the thermocline was shoaling, is unclear as we might have expected a positive chlorophyll response to an increased supply of nutrients in the photic layer associated with shallow thermocline. The skipjack purse seine CPUEs on associated sets, in the Somali basin during July-September, are distributed in chlorophyll-enriched areas resulting from the upwelling. In 2010-2012, the position of the 0.4 mg.m-3 isoline of chlorophyll concentration delineated the eastward boundary of t he skipjack CPUEs.

Statutory body / Meeting title Indian Ocean Tuna Commission (IOTC)

Meeting symbol IOTC-2013-WPTT15-09

Meeting Session Number 15

Language English