Coccolithophore dynamics in non-bloom conditions during late summer in the central Iceland Basin (July-August 2007)

Abstract

Measurements of primary production (PP), calcification (CF), and coccolithophore abundance were made
during late summer (July–August 2007) in the Iceland Basin. Low numbers of coccolithophore cells and detached
coccoliths (, 1 3 103 cells mL21 and 1–15 3 103 coccoliths mL21, respectively) indicated a non-bloom community,
with Emiliania huxleyi as the dominant coccolithophore in terms of abundance, coccolithophore organic biomass,
and cell calcite. PP ranged from 0.1 to 2 mmol C m23 d21, while CF ranged from 10 to 250 mmol C m23 d21, with
both typically decreasing with depth. Coccolithophores were estimated to contribute 10–20% toward total
chlorophyll a, phytoplankton carbon, and PP within the euphotic zone. In these non-bloom conditions, , 30–60%
of the total calcite in the water column was present as detached coccoliths rather than whole cells. Both cell numbers
and variability in cell-normalized CF controlled the magnitude of total CF, and hence both physiological limits to
cell CF and growth, as well as mortality factors, need to be taken into account when examining oceanic
coccolithophore communities. Combining cell-normalized CF with an estimate of coccolith calcite gave coccolith
production rates (0.4–1.8 h21) similar to those reported in the literature for laboratory cultures of E. huxleyi. None
of the factors currently associated with coccolithophore blooms (irradiance, mixed-layer depth, nitrate, phosphate,
or calcite saturation) showed a clear correlation with community or cellular CF. Hence, although mortality is likely
to control cell numbers, other factors such as trace metal (iron) availability may influence coccolithophore
physiology in the central Iceland Basin during late summer.

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