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Tides significantly affect polar coastlines by modulating ice shelf melt and modifying shelf water properties through transport and mixing. However, the effect of tides on the marine carbonate chemistry in such regions, especially around Antarctica, remains largely unexplored. We address this topic with two case studies in a coastal polynya in the south-eastern Weddell Sea, neighbouring the Ekström Ice Shelf. The case studies were conducted in January 2015 (PS89) and January 2019 (PS117), capturing semi-diurnal oscillations in the water column. These are pronounced in both physical and biogeochemical variables for PS89. During rising tide, advection of sea ice meltwater from the north-east created a fresher, warmer, and more deeply mixed water column with lower dissolved inorganic carbon (DIC) and total alkalinity (TA) content. During ebbing tide, water from underneath the ice shelf decreased the polynya's temperature, increased the DIC and TA content, and created a more stratified water column. The variability during the PS117 case study was much smaller, as it had less sea ice meltwater input during rising tide and was better mixed with sub-ice shelf water. The contrasts in the variability between the two case studies could be wind and sea ice driven, and they underline the complexity and highly dynamic nature of the system. The variability in the polynya induced by the tides results in an air–seaCO2 flux that can range between a strong sink (−24 mmol m−2 d−1) and a small source (3 mmol m−2 d −1) on a semi-diurnal timescale. If the variability induced by tides is not taken into account, there is a potential risk of overestimating the polynya's CO2 uptake by 67 % or underestimating it by 73 %, compared to the average flux determined over several days. Depending on the timing of limited sampling, the polynya may appear to be a source or a sink of CO2. Given the disproportionate influence of polynyas on heat and carbon exchange in polar oceans, we recommend future studies around the Antarctic and Arctic coastlines to consider the timing of tidal currents in their sampling strategies and analyses. This will help constrain variability in oceanographic measurements and avoid potential biases in our understanding of these highly complex systems.

Quantifying the variability of North Sea inflows and understanding the temporal variability of their physical properties are essential for understanding, modelling and managing the ecosystems of the North Sea. The Joint North Sea Information System (JONSIS) line hydrographic section crosses the path of the main inflows of Atlantic water into the northwestern North Sea. We use observations from an autonomous underwater glider to observe the inflows at high spatial and temporal resolutions. The glider completed 10 partial sections of the JONSIS line in October and November of 2013. Key water masses of the inflow are identified; their spatial distribution varies greatly from section to section. This is not apparent from long-running ship surveys of the JONSIS line, which are generally several months apart. In particular, the distribution of water of most recent Atlantic origin varies as summer stratification decays throughout autumn: at the start of the deployment it is present as a thin layer beneath the thermocline; at the end of the deployment, it occupies the full depth of the water column. Thermohaline flow, i.e. that which is driven by horizontal density gradients, is focused into three or four jets (approximately 10 km wide). Jets as narrow as these have not previously been observed in the region. We also observe baroclinic eddies. The thermohaline transport of the inflows is compared with the absolute transport that is derived by referencing geostrophic shear to the glider's dive-average current. Thermohaline transport (approximately 0.2 Sv) is consistently smaller than absolute transport (approximately 0.5 Sv). The week-to-week variability in hydrography and flow structure identified in this study is relevant to on-going efforts to define a background state against which the nature of anthropogenic changes can be assessed, and future modelling efforts should represent the spatial and temporal variability that we have identified.

The Ross Sea polynya is one of the most productive regions in the Southern Ocean. However, limited access and high spatio-temporal variability of physical and biological processes limit the use of conventional oceanographic methods to measure early season primary productivity. High-resolution observations from two Seagliders provide insights into the timing of a bloom in the southern Ross Sea polynya in December 2010. Changes in chlorophyll and oxygen concentrations are used to assess bloom dynamics. Using a ratio of dissolved oxygen to carbon, net primary production is estimated over the duration of the bloom showing a sensitive balance between net autotrophy and heterotrophy. The two gliders, observing spatially distinct regions during the same period, found net community production rates of -0.9±0.7 and 0.7±0.4 g C m-2 d-1. The difference highlights the spatial variability of biological processes and is probably caused by observing different stages of the bloom. The challenge of obtaining accurate primary productivity estimates highlights the need for increased observational efforts, particularly focusing on subsurface processes not resolved using surface or remote observations. Without an increased observational effort and the involvement of emerging technologies, it will not be possible to determine the seasonal trophic balance of the Ross Sea polynya and quantify the shelf’s importance in carbon export.

High-resolution autonomous glider data (including temperature, salinity, fluorescence, and optical backscatter) collected during the 2010-2011 austral summer identified variations in phytoplankton biomass along two glider sections near 76°40'S. Sea surface temperatures were warmer during the latter, westward section, while mixed layer depths were deeper. Substantial quantities of Modified Circumpolar Deep Water, identified by neutral density criteria, were located within both sections. Chlorophyll (Chl) concentrations computed from fluorescence exhibited daily quenching near the surface, and deep chlorophyll concentrations at 200. m became periodically elevated, suggesting substantial export on small space and time scales. The concentrations of particulate organic carbon (POC) computed from backscatter increased abruptly during the latter, westward section, concurrent with a decrease in chlorophyll. These higher POC:Chl ratios were not strongly correlated with presence of MCDW or with shallower mixed layer depths, but were strongly associated with higher surface temperatures and wind speed. The observed POC:Chl increase suggests a marked spatial and temporal transition between a Phaeocystis antarctica-dominated assemblage characterized by modest POC:Chl ratios to a diatom-dominated assemblage. Finally, a subsampling analysis highlights the capability of high-resolution glider data to resolve these biological/physical parameter correlations that are not discernible from lower frequency data typical of traditional cruise stations. © 2014 The Authors.