Dissolved Al during GEOTRACES Pacific Meridional Transect in the North Pacific Ocean

During the September-November 2018 U.S. GEOTRACES Pacific Meridional Transect (PMT) expedition (from Alaska to Tahiti along 152ºW), 846 water column samples were collected at 41 stations using the GEOTRACES trace element-clean rosette and the GEO-fish sampling system. These samples were filtered through a 0.2 µm AcroPak filter and were determined for dissolved Al, Fe, and Mn using shipboard Flow Injection Analysis. Strongly enhanced surface dAl values were seen between 35ºN and the equator indicating preferential dust deposition in this area, which was also seen during the CLIVAR P16N section in 2005. However, PMT dAl values were significantly higher than P16N values, between 22-23ºN and between 2-8ºN, suggesting strong variability in this region. Upwelling at the equator leads to lower surface dAl values there, with a slight increase in surface waters to the south of this region. Elevated dAl values (up to 6nM) were seen within the shallow Equatorial Under Current (EUC), very similar to the values observed during CLIVAR P16N (2005), Biocomplexity (2005) and the Japanese KH-05-2 cruises. Although the Pacific deep waters to the north of 27ºN show very low dAl (<1nM), south of 27ºN bottom waters increase to dAl value of 4-5nM. This is coincident with the presence of Circumpolar Deep Water (CDW) which is seen in both the oxygen and silicate distributions below 4000m depth. The sources of the elevations in both the surface and deep waters will be discussed.