Characterizing Spatial Variability of Ice Algal Chlorophyll a and Net Primary Production between Sea Ice Habitats Using Horizontal Profiling Platforms

Abstract

Assessing the role of sea ice algal biomass and primary production for polar ecosystems remains challenging due to the strong spatio-temporal variability of sea ice algae. Therefore, the spatial representativeness of sea ice algal biomass and primary production sampling remains a key issue in large-scale models and climate change predictions of polar ecosystems. To address this issue, we presented two novel approaches to up-scale ice algal chl a biomass and net primary production (NPP) estimates based on profiles covering distances of 100 to 1,000 s of meters. This was accomplished by combining ice core-based methods with horizontal under-ice spectral radiation profiling conducted in the central Arctic Ocean during summer 2012. We conducted a multi-scale comparison of ice-core based ice algal chl a biomass with two profiling platforms: a remotely operated vehicle and surface and under ice trawl (SUIT). NPP estimates were compared between ice cores and remotely operated vehicle surveys. Our results showed that ice core-based estimates of ice algal chl a biomass and NPP do not representatively capture the spatial variability compared to the remotely operated vehicle-based estimates, implying considerable uncertainties for pan-Arctic estimates based on ice core observations alone. Grouping sea ice cores based on region or ice type improved the representativeness. With only a small sample size, however, a high risk of obtaining non-representative estimates remains. Sea ice algal chl a biomass estimates based on the dominant ice class alone showed a better agreement between ice core and remotely operated vehicle estimates. Grouping ice core measurements yielded no improvement in NPP estimates, highlighting the importance of accounting for the spatial variability of both the chl a biomass and bottom-ice light in order to get representative estimates. Profile-based measurements of ice algae chl a biomass identified sea ice ridges as an underappreciated component of the Arctic ecosystem Lange et al.Ice-Algal Biomass and NPP because chl a biomass was significantly greater in this unique habitat. Sea ice ridges are not easily captured with ice coring methods and thus require more attention in future studies. Based on our results, we provide recommendations for designing an efficient and effective sea ice algal sampling program for the summer season.

Algal Hot Spots in a Changing Arctic Ocean: Sea-Ice Ridges and the Snow-Ice Interface

“…This transmittance values were similar to those measured below ridges by an ROV in the Central Arctic (up to 5%) (Lange et al, 2017b), and lower than the PAR transmittance in the thin ice next to the ridge (5-40%) . However, in situ measurements below the snow might be affected by lateral spreading of radiation and light scatter when removing part of the snow cover to introduce the sensor.…”

“…Nevertheless, compared to other sea-ice environments (FYI, new, and young ice), ridges and deformed ice areas, can account for most of the sea-ice related biomass. This is in agreement with large-scale under-ice ROV surveys that point toward ridges as relevant for algal biomass accumulation (Lange et al, 2017b). It is therefore critical that ridges are examined more closely and included in biomass and productivity estimates for Arctic sea ice.…”

“…Ridges are known to be hot spots for biological activity since they act as shelters for ice fauna and ice-associated zooplankton (Hop and Pavlova, 2008;Gradinger et al, 2010) and juvenile polar cod (Gulliksen and Lønne, 1989). Ridges have also been recently identified as locations of high algal biomass using under-water remotely operated vehicles (Lange et al, 2017b). However, due to the sampling challenges that these complex structures pose, algae have only been sampled sporadically.…”

Chlorophyll‐a in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data

“…Furthermore, the spatial variability of Chl a in fast ice is probably not well represented by sampling a limited number of ice cores. In Arctic pack ice, ice algal biomass was significantly underestimated by ice core‐based sampling compared to under‐ice profilers measuring ice algae biomass at high resolution over hundreds of meters to kilometers of distance (Lange et al, , ). The spatial variability of ice algae biomass is often controlled by physical drivers, such as snow thickness and sea ice structure.…”

“…We further recommend increasing long‐term observations that capture the full annual cycle of fast‐ice growth and decay. The development of automated ice‐tethered observatories that combine physical (Heil et al, ; Nicolaus et al, ) and biological (Campbell et al, , ; Lange et al, , ; Meiners et al, ; Melbourne‐Thomas et al, ) sea ice measurements may become key in furthering our understanding of ice algal dynamics and its physical controls in Antarctic fast ice. As atmospheric conditions are key drivers of fast‐ice algal dynamics, research teams should increase the use of meteorological data collected at nearby coastal stations to support their data interpretation.…”