DOI: 10.5061/dryad.47d7wm391
title: Biological calcification rate and species-specific contributions of coccolithophores to total calcite inventory in the eastern Indian Ocean

description: Coccolithophores are calcifying protists that have significant role in
 marine biological pump through calcite production (CP). We determined the
 biological calcification rate and ecologically key species (e.g.
 Gephyrocapsa oceanica) contribution to total calcite stocks in the eastern
 Indian Ocean (EIO) during spring intermonsoon. This region was quite
 under-sampled compared to other oceanic regions. Our results indicated
 that the numerically dominant species are of great importance to cell
 calcite even with low cellular calcite. CP rate in EIO ranged from 0.148
 to 85.017 μmol C m⁻3 d⁻1 in the entire dataset, which was lower than those
 in the global ocean. Coccolithophores contributed 8.5% of total
 phytoplankton carbon fixation. CP acted as a function of light irradiance
 in the euphotic zone, while a decoupling between CP and primary
 productivity (PP) was found in most of the bottom of euphotic zone. To
 some degree, this decoupling indicated calcification was more
 nitrate-dependent and less light-dependent than photosynthesis. CP/PP
 ratios were highly variable in our database and were possibly influenced
 by photoacclimation across various coccolithophore species. As roughly
 estimated, the turnover rate of coccolith calcite took values around
 0.02-0.05 d⁻1. The association between particulate organic carbon (POC)
 and calcite stocks implied a potential increasing ballast as depth
 increase. The current profiles of calcification and associated
 biogeochemical elements obtained from this field study helps our
 understanding about characteristics of biological pump in the EIO and are
 valuable for estimating calcification rate in the region using satellite
 data and numerical modeling.
description: The eastern Indian Ocean (EIO) cruise took place onboard R/V
 “SHIYAN 3” during the period 27 February to 22 April 2017 spring
 inter-monsoon and consisted of 15 stations along three transects. Water
 samples were collected from a Rosette sampler system with attached Seabird
 CTD (conductivity-temperature-depth) profiler. Pressure, conductivity, and
 temperature at all designed stations were collected by means of CTD
 probes. For coccolithophore sampling, 500 ml seawater was gently filtered
 through mixed cellulose membrane (25 mm diameter, 0.22 μm) with a vacuum
 pump lower than 20 mm Hg pressure. For nutrient sampling, 100 ml seawater
 was filtered through acid-cleaned 0.45 μm pore-size acetate cellulose
 filters and then chilled at -20°C. In the laboratory, five kinds of
 nutrients (NO<sub>3</sub>⁻, NO<sub>2</sub>⁻,
 PO<sub>4</sub><sup>3−</sup>, and
 SiO<sub>3</sub><sup>2−</sup>) were analyzed using
 an Autoanalyzer 3-AA3 (Bran+ Luebbe, Norderstedt, Germany). For Chl
 <em>a</em> determination, 1000 ml seawater was filtered onto
 25 mm Whatman GF/F filters and chilled at -20°C. In the laboratory, Chl
 <em>a</em> extraction and measurement followed the procedure
 of <em>Parsons et al.</em> (1984). Radioactive carbon isotope
 was utilized to trace the inorganic carbon uptake through calcification
 process. Field seawater was collected according to five light attenuations
 (100%, 50%, 25%, 10%, and 1% of surface PAR) within euphotic layer. The
 above all biochemical parameters (section 2.2 and section 2.3) were
 sampled following the same depth layer. 200 ml seawater was transferred to
 250 ml Nalgene polycarbonate bottles. For each light level, triplicate
 light bottles and one dark bottle were incubated 6 h (from morning 10:00
 to afternoon 16:00) on deck spiked with 10-20 μCi 14C-labelled
 NaH<sup>14</sup>CO<sub>3</sub>. After incubation,
 the samples were filtered gently through GF/F filters (Whatman 25 mm) and
 then rinsed with GF/F filtered-seawater three times. The filters were then
 kept in 20 ml scintillation vials under cool storage.
description: # Biological calcification rate and species-specific contributions of
 coccolithophores to total calcite inventory in the eastern Indian Ocean
 Dataset DOI:
 [10.5061/dryad.47d7wm391](https://doi.org/10.5061/dryad.47d7wm391) ##
 Description of the data and file structure All data were derived from
 field investigation, and there are some missing values during measurement.
 ##