TY - JOUR
T1 - Phytoplankton Community Structure and Depth Distribution Changes in the Cariaco Basin between 1996 and 2010
AU - Pinckney, J. L
AU - Benitez-Nelson, C. R
AU - Thunell, R. C
AU - Muller-Karger, Frank E
AU - Lorenzoni, Laura
AU - Troccoli, L.
AU - Varela, R.
PY - 2015/1/1
Y1 - 2015/1/1
N2 - Phytoplankton community structure at the Cariaco Basin Time-Series site (10°30'N, 64°40'W) within the Cariaco Basin was examined using high performance liquid chromatography (HPLC) and microscopy between January 1996 to October 2000, and July 2006 to December 2010. Microscopy results from the upper 55. m indicated that the abundance of microphytoplankton (>20. μm) decreased by more than 5-fold from 1996 through 2010, accompanied by a change in diatom composition and a 4-fold reduction in large diatom cell numbers, particularly during upwelling periods. HPLC results also indicate a decline in diatoms, but not nearly to the same extent. Rather, HPLC data suggests a substantial reorganization of the phytoplankton community. Between the two time periods, there was a significant deepening of high biomass concentrations from near surface waters to depths below 55. m. At the same time, phytoplankton diversity increased by 14%, while seasonal variability in community composition declined. Vertical photopigment distributions of nanophytoplankton (<20. μm) further showed significant overall increases in coccolithophore, cryptophyte, and other phytoflagellate concentrations. The deepening in phytoplankton biomass below the mixed layer, the relative increase in smaller taxa, and the increasing homogeneity in phytoplankton distributions over time are likely a direct response to a reduction in upwelling intensity and a deepening of the euphotic zone associated with a decrease in the average trade winds of the region from 2006-2010, compared to 1996-2000. Surprisingly, the overall decline in large cells dominated by diatoms and an increase in smaller taxa has led to no significant change in the export of particulate organic carbon (POC) to depth, contrary to many studies that predict increasing stratification with future climate change scenarios will reduce POC export and carbon sequestration in the deep ocean.
AB - Phytoplankton community structure at the Cariaco Basin Time-Series site (10°30'N, 64°40'W) within the Cariaco Basin was examined using high performance liquid chromatography (HPLC) and microscopy between January 1996 to October 2000, and July 2006 to December 2010. Microscopy results from the upper 55. m indicated that the abundance of microphytoplankton (>20. μm) decreased by more than 5-fold from 1996 through 2010, accompanied by a change in diatom composition and a 4-fold reduction in large diatom cell numbers, particularly during upwelling periods. HPLC results also indicate a decline in diatoms, but not nearly to the same extent. Rather, HPLC data suggests a substantial reorganization of the phytoplankton community. Between the two time periods, there was a significant deepening of high biomass concentrations from near surface waters to depths below 55. m. At the same time, phytoplankton diversity increased by 14%, while seasonal variability in community composition declined. Vertical photopigment distributions of nanophytoplankton (<20. μm) further showed significant overall increases in coccolithophore, cryptophyte, and other phytoflagellate concentrations. The deepening in phytoplankton biomass below the mixed layer, the relative increase in smaller taxa, and the increasing homogeneity in phytoplankton distributions over time are likely a direct response to a reduction in upwelling intensity and a deepening of the euphotic zone associated with a decrease in the average trade winds of the region from 2006-2010, compared to 1996-2000. Surprisingly, the overall decline in large cells dominated by diatoms and an increase in smaller taxa has led to no significant change in the export of particulate organic carbon (POC) to depth, contrary to many studies that predict increasing stratification with future climate change scenarios will reduce POC export and carbon sequestration in the deep ocean.
KW - Caribbean Sea
KW - ChemTax
KW - Climate change
KW - Diversity index
KW - HPLC
KW - Phytoplankton community
UR - https://digitalcommons.usf.edu/msc_facpub/1038
UR - http://10.1016/j.dsr.2015.03.004
U2 - 10.1016/j.dsr.2015.03.004
DO - 10.1016/j.dsr.2015.03.004
M3 - Article
VL - 101
JO - Deep-Sea Research Part I: Oceanographic Research Papers
JF - Deep-Sea Research Part I: Oceanographic Research Papers
ER -