The global distribution of pteropods and their contribution to carbonate and carbon biomass in the modern ocean

Abstract

Abstract. Pteropods are a group of holoplanktonic gastropods for which global biomass distribution patterns remain poorly described. The aim of this study was to collect and synthesise existing pteropod (Gymnosomata, Thecosomata and Pseudothecosomata) abundance and biomass data, in order to evaluate the global distribution of pteropod carbon biomass, with a particular emphasis on temporal and spatial patterns. We collected 25 939 data points from several online databases and 41 scientific articles. These data points corresponded to observations from 15 134 stations, where 93% of observations were of shelled pteropods (Thecosomata) and 7% of non-shelled pteropods (Gymnosomata). The biomass data has been gridded onto a 360 × 180° grid, with a vertical resolution of 33 depth levels. Both the raw data file and the gridded data in NetCDF format can be downloaded from PANGAEA, doi:10.1594/PANGAEA.777387. Data were collected between 1950–2010, with sampling depths ranging from 0–2000 m. Pteropod biomass data was either extracted directly or derived through converting abundance to biomass with pteropod-specific length to carbon biomass conversion algorithms. In the Northern Hemisphere (NH), the data were distributed quite evenly throughout the year, whereas sampling in the Southern Hemisphere (SH) was biased towards winter and summer values. 86% of all biomass values were located in the NH, most (37%) within the latitudinal band of 30–60° N. The range of global biomass values spanned over four orders of magnitude, with mean and median (non-zero) biomass values of 4.6 mg C m−3 (SD = 62.5) and 0.015 mg C m−3, respectively. The highest mean biomass was located in the SH within the 70–80° S latitudinal band (39.71 mg C m−3, SD = 93.00), while the highest median biomass was in the NH, between 40–50° S (0.06 mg C m−3, SD = 79.94). Shelled pteropods constituted a mean global carbonate biomass of 23.17 mg CaCO3 m−3 (based on non-zero records). Total biomass values were lowest in the equatorial regions and equally high at both poles. Pteropods were found at least to depths of 1000 m, with the highest biomass values located in the surface layer (0–10 m) and gradually decreasing with depth, with values in excess of 100 mg C m−3 only found above 200 m depth. Tropical species tended to concentrate at greater depths than temperate or high-latitude species. Global biomass levels in the NH were relatively invariant over the seasonal cycle, but more seasonally variable in the SH. The collected database provides a valuable tool for modellers for the study of marine ecosystem processes and global biogeochemical cycles. By extrapolating regional biomass to a global scale, we established global pteropod biomass to add up to 500 Tg C.