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The Great Calcite Belt (GCB) is a band of high concentrations of suspended particulate inorganic carbon (PIC) spanning the subantarctic Southern Ocean and plays an important role in the global carbon cycle. The key limiting factors controlling coccolithophore growth supporting this high PIC have not yet been well‐characterized in the remote Pacific sector, the lowest PIC but largest area of the GCB. Here, we present in situ physical and biogeochemical measurements along 150°W from January to February 2021, where a coccolithophore bloom occurred. In both months, PIC was elevated in the Subantarctic Zone (SAZ), where nitrate was >1 μM and temperatures were ∼13°C in January and ∼14°C in February, consistent with conditions previously associated with optimal coccolithophore growth potential. The highest PIC was associated with a relatively narrow temperature range that increased about 1°C between occupations. A fresher water mass had been transported to the 150°W meridian between occupations, and altimetry‐informed Lagrangian backtracking estimates show that most of this water was likely transported from the southeast within the SAZ. Applying the observations in a coccolithophore growth model for both January and February, we show that the ∼1.7°C increase in temperature can explain the rise in PIC between occupations. Coccolithophore concentrations rose in the Subantarctic Zone in the Pacific sector of the Southern Ocean between January and February 2021Lagrangian particle tracking suggests that the coccolithophore‐associated surface waters observed in February came from the southeastModeling suggests the ∼1.7°C warming can explain the coccolithophore growth in the Subantarctic Zone between occupations Coccolithophore concentrations rose in the Subantarctic Zone in the Pacific sector of the Southern Ocean between January and February 2021 Lagrangian particle tracking suggests that the coccolithophore‐associated surface waters observed in February came from the southeast Modeling suggests the ∼1.7°C warming can explain the coccolithophore growth in the Subantarctic Zone between occupations

A new algorithm for estimating particulate inorganic carbon (PIC) concentrations from ocean color measurements is presented. PIC plays an important role in the global carbon cycle through the oceanic carbonate pump, therefore accurate estimations of PIC concentrations from satellite remote sensing are crucial for observing changes on a global scale. An extensive global data set was created from field and satellite observations for investigating the relationship between PIC concentrations and differences in the remote sensing reflectance (Rrs) at green, red, and near‐infrared (NIR) wavebands. Three color indices were defined: two as the relative height of Rrs(667) above a baseline running between Rrs(547) and an Rrsin the NIR (either 748 or 869 nm), and one as the difference between Rrs(547) and Rrs(667). All three color indices were found to explain over 90% of the variance in field‐measured PIC. But, due to the lack of availability of Rrs(NIR) in the standard ocean color data products, most of the further analysis presented here was done using the color index determined from only two bands. The new two‐band color index algorithm was found to retrieve PIC concentrations more accurately than the current standard algorithm used in generating global PIC data products. Application of the new algorithm to satellite imagery showed patterns on the global scale as revealed from field measurements. The new algorithm was more resistant to atmospheric correction errors and residual errors in sun glint corrections, as seen by a reduction in the speckling and patchiness in the satellite‐derived PIC images. The oceans are full of plant life which provides food for all the larger animals in the oceans. This plant life is really small and you can only see individual plants with a microscope. However, when there is a lot of this plant life in one place, it can change the color of the ocean so much that we can see it from a ship, a plane or even from satellites. We call these plants algae, or phytoplankton. Just like on the land, where there are lots of different types of plant, there are lots of different types of phytoplankton. We are interested in one particular type, which has a chalk outer shell, causing the ocean to turn a milky blue when there are lots of them growing together. These chalk covered phytoplankton play a major role in regulating carbon in the oceans, and so it is important to know both where these phytoplankton are and how many of them there are. We have developed a new way to estimate how much chalk is in the ocean from satellite observations to help us estimate where these chalk covered phytoplankton are. Extensive field observations are used to develop a new particulate inorganic carbon algorithmThe new algorithm provides more accurate estimation of PIC compared to the standard algorithmWhite cap, sun glint, and atmospheric correction error artifacts are reduced in satellite imagery

We report surface observations of a mesoscale coccolithophore bloom at the shelf break of the Patagonian Shelf during December 2008, representing the densest coccolithophore population in the Southern Ocean. The bloom was most intense within the Falklands Current, northeast of the Falkland Islands. Emiliania huxleyidominated bloom waters, with a mixed E. huxleyiand Prorocentrumsp. dinoflagellate bloom to the west and mixed assemblage of diatoms, dinoflagellates, and flagellates to the east. Optical measurements of coccolith light scattering, analytical measurements of their calcite, and microscopic counts all showed this to be an intense coccolithophore bloom. Average particulate inorganic carbon per coccolith in the bloom was low, typical of the B coccolith morphotype and in agreement with independent measurements made by scanning electron microscopy. Highest particulate inorganic carbon (measured optically and chemically) was observed when residual nitrate (defined as the difference, [NO3−1] − [Si(OH)4]) was 10–17 µmol L−1and nitrate to phosphate ratios were close to Redfield values. Elevated particle backscattering was observed in the E. huxleyibloom, whereas the highest particle scattering occurred in the adjoining Prorocentrumsp. bloom. Backscattering from coccolithophores represented up to 50% of the total backscattering (from organic and inorganic particles) along the main axis of the E. huxleyibloom. Chlorophyll‐specific absorption in the coccolithophore bloom was typical of marine phytoplankton. Residual nitrate plotted vs. temperature showed that the E. huxleyibloom was associated with waters between 5°C and 15°C, with depleted silicate. Results suggest that previous drawdown of silicate by diatoms occurred prior to the densest E. huxleyiblooms over the Patagonian Shelf. We speculate that such conditions might also be important for annual development of the broader Great Calcite Belt and other coccolithophore blooms..