A meeting place of great ocean currents: Shipboard observations of a convergent front at 2°N in the Pacific
Document Type
Article
Date of Original Version
12-1-1997
Abstract
We present a synthesis of physical, chemical and biological shipboard observations of a convergent front at 2°N, 140°W and its surrounding environment. The front was a component of a tropical instability wave generated by shear between westward-flowing equatorial waters to the south and warmer equatorial counter current water to the north. Surface waters on the cold side were undersaturated with oxygen, which suggests that the water had only been exposed at the sea surface for a period of a few weeks. Although the atmospheric exposure time was short, the effects of biological activity could be detected in enhanced concentrations of total (dissolved plus suspended particulate) organic carbon concentration, proving that TOC can be produced quickly in response to changing environmental conditions. The front itself was dominated by the accumulation of a 'patch' of buoyant diatoms Rhizosolenia castracanei concentrated in the top centimeters of the warm surface water north of the front, and elevated chlorophyll concentrations were observed from the air over a spatial scale of order 10-20 km northward from the front. The nitrogen budget and thorium data suggest that a significant fraction of the elevated POC, and virtually all of the PON, arrived in the patch waters as imported particles rather than in situ photosynthesis. Photosynthetic uptake of carbon appears to have occurred in patch waters, but without corresponding uptake of fixed nitrogen (an uncoupling of the usual Redfield stoichiometry). Solute chemistry of the patch appears to be controlled by turbulent mixing, which flushes out patch waters on a time scale of days (faster than atmospheric ventilation.) The subduction of nutrient-rich equatorial surfaces water below the front was detected 100 km north of the front in the signatures of temperature, salinity and ammonium.
Publication Title, e.g., Journal
Deep-Sea Research Part II: Topical Studies in Oceanography
Volume
44
Issue
9-10
Citation/Publisher Attribution
Archer, David, Jim Aiken, William Balch, Dick Barber, John Dunne, Pierre Flament, Wilford Gardner, Chris Garside, Catherine Goyet, Eric Johnson, David Kirchman, Michael McPhaden, Jan Newton, Edward Peltzer, Leigh Welling, Jacques White, and James Yoder. "A meeting place of great ocean currents: Shipboard observations of a convergent front at 2°N in the Pacific." Deep-Sea Research Part II: Topical Studies in Oceanography 44, 9-10 (1997). doi: 10.1016/S0967-0645(97)00031-3.