Airborne bio-optics survey of the Galapagos Islands margins

Aircraft and ship surveys of the Galapagos Islands were conducted to address the hypothesized influence of “island-leached” iron upon phytoplankton production. This paper describes the airborne survey of the Galapagos Islands that composed the second phase of a two-part study of the influence of iron on phytoplankton production in high-nutrient/low-chlorophyll (HNLC) regions. A single bio-optics airborne survey transect along 92°W from 1°N to 2°S was executed on 25 October 1993 in order to provide initial reconnaissance spatial and temporal sampling of the oceanic region west of the Galapagos Islands. A more extensive airborne bio-optics survey of the entire Galapagos Islands region was conducted on 3 November 1993. This expanded flight survey was made along all the ship cruise tracks of the R.V. Columbus Iselin originally planned for 15–27 November 1993. is of the surface-layer airborne laser-induced and water-Raman normalized chlorophyll, phycoerythrin, and chromophoric dissolved organic matter (CDOM) fluorescence, SST, and AXBT (airborne expendable bathythermograph) data suggest that: (1) the regional distribution of phytoplankton and dissolved organic matter is dominated by the strong east–west thermal boundary located both east and west of the Galapagos Islands; (2) the source for the elevated phytoplankton patches west of the Galapagos Islands is from upwelling rather than aeolian sources or from the westward drift of iron and nutrients leached from the islands themselves or offshore shallow bottom sources; (3) the introduction of subsurface water to the surface may occur in episodic events rather than as a steady-state process; and (4) the chronic high chlorophyll west of the Galapagos Islands noted in processed Coastal Zone Color Scanner (CZCS) images may be due, at least in part, to the presence of elevated levels of chromophoric dissolved organic matter (CDOM) absorption.