Abstract
Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs, and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using 14C-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed, and 449 stations occupied where measurements of primary productivity (each with 7 depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 ± 1.20 g C m−2 d−1, and the maximum was 13.1 g C m−2 d−1. Annual productivity calculated from the means throughout the growing season equalled 146 g C m−2 yr−1. Mean chlorophyll concentration in the euphotic zone (the 1 % irradiance level) was 2.85 ± 2.68 mg m−3 (maximum concentration was 19.1 mg m−3). Maximum photosynthetic rates at the surface (normalized to chlorophyll) averaged 0.94 ± 0.71 mg C (mg chl)−1 h−1, similar to the maximum rate found in photosynthesis/irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica, and summer productivity by diatoms. The data set will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity.
Highlights
IntroductionA quantitative assessment of the ocean’s primary productivity (the rate at which carbon dioxide is reduced to organic matter by marine phytoplankton photosynthesis) is a critical variable in understanding the ecology and biogeochemistry in marine systems
Maximum photosynthetic rates at the surface averaged 0.94 ± 0.71 mg C-1 h-1, similar to the maximum rate found in photosynthesis/irradiance measurements
Assimilation numbers were relatively uniform throughout the upper euphotic zone, and for the 100, 50 and 30% isolumes averaged 0.98 mg C-1 h-1 (Fig. 2), similar to the maximum 170 photosynthetic rate compiled for the Ross Sea continental shelf from photosynthesis/irradiance experiments (1.10 mg C-1 h-1; Smith and Donaldson, 2015)
Summary
A quantitative assessment of the ocean’s primary productivity (the rate at which carbon dioxide is reduced to organic matter by marine phytoplankton photosynthesis) is a critical variable in understanding the ecology and biogeochemistry in marine systems. The ocean is far too large to measure productivity synoptically, and as a result numerous bio-optical 40 models have been derived to estimate primary productivity using remotely sensed information (temperature, chlorophyll concentrations, irradiance; e.g., Behrenfeld and Falkowski, 1997a,b). These models have enabled oceanographers to estimate productivity on large space and time scales, and have been used in more restricted analyses of productivity (Mouw and Yoder, 2005; Smith et al, 2021; Oliver et al, 2021). Two critical aspects of the original Behrenfeld and Falkowski (1997a,b) models were based on results from primary productivity measurements that used 14C-uptake – the relationship between the 45 maximum rate of photosynthesis as a function of temperature (fitted to a 7th-order polynomial) and the photoinhibition estimate
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
