FLUORESCENCE SIGNATURES OF AN IRON-ENRICHED PHYTOPLANKTON COMMUNITY IN THE EASTERN EQUATORIAL PACIFIC-OCEAN

Laser-induced fluorescence profiles of chlorophyll and phycoerythrin p igments and chromophoric dissolved organic matter (CDOM) fluorescence acquired over an iron-enriched phytoplankton patch are compared to pro files made over adjacent, naturally occurring phytoplankton patches. A total of four airborne missions were flown during an 8 day period fol lowing the release of the iron-rich fertilizer. Analyses of the airbor ne laser-induced fluorescence profiles from the upper-ocean layer reve al: (1) Ship-dispersed iron enhances localized phytoplankton productio n in high-nutrient/low-chlorophyll regions such as found in the easter n equatorial Pacific Ocean. (2) The chlorophyll concentration within t he iron-enriched phytoplankton patch exceeded levels of chlorophyll fo und in naturally occurring phytoplankton patches located outside the e nriched region. (3) An increase in phycoerythrin fluorescence was obse rved within the enriched region in correspondence with the elevated ch lorophyll fluorescence. However, the phycoerythrin/chlorophyll fluores cence ratio was lower within the enriched patch than in naturally occu rring phytoplankton patches outside of the enriched region. (4) No abo ve-background chromorophoric dissolved organic matter (CDOM) fluoresce nce was observed in the enriched patch. Elevated CDOM fluorescence was associated with some of the naturally occurring phytoplankton patches outside the enriched region, while other such phytoplankton patches s howed no measurable increase in CDOM over background levels. (5) The s urface layer manifestation of the patch was observed to be transported to the north and west in close agreement with the drogue positions. N o elevated surface layer chlorophyll fluorescence was seen in the vici nity of the ship as it sampled the submerged fraction at the time of t he 30 October and I November overflights. The phycoerythrin pigment fl uorescence emission was insensitive to ambient cloud-induced downwelli ng irradiance variability, while at the same time the chlorophyll fluo rescence displayed considerable quenching for which corrections were m ade using the airborne downwelling irradiance. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.