The Solomon Sea: its circulation, chemistry, geochemistry and biology explored during two oceanographic cruises

Alexandre Ganachaud,Cyril Germineaud,Nicolas Metzl,Marc Souhaut,Mar Benavides,Jérôme Lefèvre,Janet Sprintall,Susanna Michael,Catherine Jeandel,Fabien Quéroué,Géraldine Sarthou,Sophie Bonnet,Uwe Send,Sophie Cravatte,Jacques Grelet,Marion Alberty,Moyep Kilepak,François Baurand,Takuya Hasegawa,Jeroen E Sonke,Hugo Berthelot,Pieter Van Beek,Emilien Privat,Martine Rodier,F Lacan ,Gérard Eldin ,William S Kessler ,J A Resing ,Lars-Éric Heimbürger

doi:10.1525/elementa.221

Abstract

The semi-enclosed Solomon Sea in the southwestern tropical Pacific is on the pathway of a major oceanic circuit connecting the subtropics to the equator via energetic western boundary currents. Waters transiting through this area replenish the Pacific Warm Pool and ultimately feed the equatorial current system, in particular the equatorial undercurrent. In addition to dynamical transformations, water masses undergo nutrient and micronutrient enrichment when coming in contact with the coasts, impacting the productivity of the downstream equatorial region. Broadscale observing systems are not well suited for describing the fine-scale currents and water masses properties in the Solomon Sea, leaving it relatively unexplored. Two multidisciplinary oceanographic cruises were conducted in the Solomon Sea region, the first in July–August 2012 and the second in March 2014, by investigators from France and the United States. The experimental approach combined physical, chemical, geochemical and biogeochemical analyses, providing access to a wide range of space and time scales of the circulation. This collection of data allows describing the fine-scale structure of the currents and the water properties, transformations and mixing from the surface to the sill depth in the Solomon Sea and in the straits connecting it to the equator. Ocean-margin exchanges were documented through a comprehensive sampling of trace elements and isotopes as efficient tracers of natural fertilization processes. As air chemistry is largely impacted by the regional volcanic plumes, rainwater pH was also sampled. Dinitrogen fixation rates were measured and found to be among the highest in the global ocean, highlighting this region as a hot spot of nitrogen fixation. This study provides an overview of the climatic context during both cruises and the physical circulation and water masses properties. It provides a comprehensive description of all measurements made onboard, and presents preliminary results, aiming to serve as a reference for further physical, geochemical and biogeochemical studies.

Highlights

The Solomon Sea is a semi-enclosed sea located at the western boundary of the equatorial Southwest Pacific Ocean, between Papua New Guinea and the Solomon Islands (Figure 1)
All previous works agree on the following mean circulation pattern: the bulk of thermocline transport into the Solomon Sea enters through the southern opening of the Solomon Sea where the Gulf of Papua Current joins the North Vanuatu Jet (NVJ) in forming the low latitude western boundary current called the New Guinea Coastal Undercurrent (NGCU) (Figure 1); (e.g., Melet et al, 2010; Gasparin et al, 2012; Kessler and Cravatte, 2013)
Sea surface waters in the Solomon Sea appeared to be saltier and colder during Pandora compared to MoorSPICE (Figure 5) except northeast of Bougainville Island

Summary

Introduction

The Solomon Sea is a semi-enclosed sea located at the western boundary of the equatorial Southwest Pacific Ocean, between Papua New Guinea and the Solomon Islands (Figure 1). Suspecting the importance of the Solomon Sea circulation to the general Pacific circulation, Lindstrom et al (1987) made two surveys in 1985 and 1986 that revealed large and vigorous transports toward the equator This region appeared as an essential pathway for waters originating from mid-to high latitudes and joining the western equatorial Pacific and the equatorial current system. All previous works agree on the following mean circulation pattern: the bulk of thermocline transport into the Solomon Sea enters through the southern opening of the Solomon Sea where the Gulf of Papua Current joins the North Vanuatu Jet (NVJ) in forming the low latitude western boundary current called the New Guinea Coastal Undercurrent (NGCU) (Figure 1); (e.g., Melet et al, 2010; Gasparin et al, 2012; Kessler and Cravatte, 2013). The circulation in the Solomon Sea and straits is quasi unknown

Objectives

Results

Conclusion