Cruise Report Protected Area Sea Education Association Cruises S-254, S-261

Scientific data collected aboard SSV Robert C. Seamans

Honolulu, Hawaii – Enderbury – Kanton – - - Pago Pago, American Samoa

1 July-13 August 2014 6 July-14 August 2015

Sea Education Association Woods Hole, Massachusetts Citation: Witting, Jan, 2016. Final Report for S.E.A. cruise S-254 and S-261. Sea Education Association, P.O. Box 6, Woods Hole, MA 02543, USA.

To obtain unpublished data, contact the Chief Scientist or the SEA Data Archivist: Data Archivist Sea Education Association P.O. Box 6 Woods Hole, MA 02543

Phone: 508-540-3954 Fax: 508-457-4673 E-mail: [email protected] Web: www.sea.edu Executive Summary.

The Phoenix Islands Protected Area (PIPA) is one of the largest investments ever made in the protection of the marine environment. While the eight islands with their remarkable reef ecosystems of the Phoenix Islands archipelago have been described to some detail during six coral reef research expeditions, the oceanography and the pelagic ecosystem of the area remains largely unstudied. To start remedying this gap in our knowledge, the Sea Education Association (SEA) of Woods Hole, MA, in association with the New England Aquarium and the Woods Hole Oceanographic Institution conducted two research cruises to PIPA in July-August of 2014 and 2015 using SEA’s sailing research vessel the Robert C. Seamans. Both expeditions spent three weeks in the PIPA waters, conducting extensive water column sampling for oceanographic parameters ranging from temperature and salinity to ocean chemistry, currents and zooplankton abundance.

While the 2014 was intended to be generate the first synoptic view of the conditions within PIPA in the Austral winter, it was also meant to begin a series of repeated surveys to document the annual and inter annual changes in the ocean conditions there. Being close to the equator, the largest changes in the oceanography here is not seasonal, but due to the El Niño-Southern Oscillation (ENSO) cycle, a coupled ocean/atmosphere phenomenon leading to changes in the surface ocean that range between a warm, (El Niño) and a cool state (La Niña). As the luck would have it, the second expedition in 2015 headed into one of the largest El Niño periods on record, and was able to capture the difference in the state of PIPA in ENSO neutral (2014) and El Niño conditions.

The 2014 results showed that PIPA straddles the transition between equatorial waters of the equatorial upwelling zone, dominated in the Southern Hemisphere by the swift, eastward flowing equatorial counter current (EUC). The effects of the mixing of sub-thermocline water to the surface can be seen across the board from temperature and density to nutrient concentrations and elevated primary productivity. The effects of this enrichment were felt from the northern boundary to Kanton. Between Kanton and Orona there was a another area of high primary productivity as measured by chlorophyll a concentration, though the mechanism for this phenomenon is less clear.

The 2015 results show a very different transition. Whereas in 2014 the sea surface temperature rose from north to south (equatorial upwelling influence), the 2015 showed no clear zonal pattern with surface temperatures 2˚C higher on the average and across the board. This led to much increased density stratification and reduced mixing that resulted in drastic reduction in the availability of nutrients in the mixed layer, and equally dramatic shut-down of primary productivity in waters from the northern boundary down to around Kanton-Nikumaroro line. However, from Nikumaroro south, primary productivity increases to levels comparable to 2014, and this likely due to the influence of another p