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Sea ice core chlorophyll a data are used to describe the seasonal, regional and vertical distribution of algal biomass in Southern Ocean pack ice. The Antarctic Sea Ice Processes and Climate – Biology (ASPeCt – Bio) circumpolar dataset consists of 1300 ice cores collected during 32 cruises over a period of 25 years. The analyses show that integrated sea ice chlorophyll apeaks in early spring and late austral summer, which is consistent with theories on light and nutrient limitation. The results indicate that on a circum‐Antarctic scale, surface, internal and bottom sea ice layers contribute equally to integrated biomass, but vertical distribution shows distinct differences among six regions around the continent. The vertical distribution of sea ice algal biomass depends on sea ice thickness, with surface communities most commonly associated with thin ice (<0.4 m), and ice of moderate thickness (0.4–1.0 m) having the highest probability of forming bottom communities. Key Points Antarctic sea ice chlorophyll a shows maxima in early spring and late summer Surface, internal and bottom ice layers contribute equally to integrated biomass The vertical distribution of chlorophyll a critically depends on ice thickness

A time series experiment was conducted in late austral spring (November–December 2009) in coastal fast ice, East Antarctica (66°13′07″S, 110°39′02″E). Iron (Fe) measurements were made in sea ice, snow, brines, and underlying seawater, together with meteorological, physical, and biogeochemical measurements to investigate the processes controlling the release of Fe into the underlying water column. Warming air temperatures were clearly associated with decreasing brine volume fractions. Macronutrient profiles revealed very low (<1 μM) nitrate + nitrite concentrations in the interior of the sea ice, and the brines suggested nitrate + nitrite drawdown exceeded Redfield ratios in comparison to phosphate and silicate. In the basal ice, nitrate + nitrite and silicate were drawn down through time but did not lead to a limiting condition. We found that dissolved Fe tracked the brine volume fraction and was readily transferred from the surface/interior to the underlying water column over time. In contrast, particulate Fe did not show this clear decreasing trend and correlated with particulate organic carbon and chlorophyll a distributions. Over the 28 d of sampling, two distinct mean air temperature warming events were observed (−12.1 to −1.3°C and −6.4 to 0.8°C). This resulted in the release of 419 μmol of TDFe per m2 of sea ice from our coastal fast ice station into the underlying water column during the study period. Assuming an increase of 1 nM Fe is sufficient for Antarctic diatoms to bloom, our study site presented a fertilization potential for 419 m3 of Fe limited surface Southern Ocean seawater with TDFe and 29 m3 with dFe, per m2 of fast ice. Key Points Fast ice is a significant substrate for iron storage and seawater fertilization Release of dissolved Fe but not particulate Fe controlled by brine volume Warming air temperatures were clearly associated with decreasing brine volume

The presence of algal pigments in sea ice alters under-ice irradiance spectra, and the relationship between these variables can be used as a non-invasive means for estimating ice-associated algal biomass on ecologically relevant spatial and temporal scales. While the influence of snow cover and ice algal biomass on spectra transmitted through the snow-ice matrix has been examined for the Arctic, it has not been tested for Antarctic sea ice at regional scales. We used paired measurements of sea ice core chl a concentrations and hyperspectral-transmitted under-ice irradiances from 59 sites sampled off East Antarctica and in the Weddell Sea to develop algorithms for estimating algal biomass in Antarctic pack ice. We compared 4 approaches that have been used in various bio-optical studies for marine systems: normalised difference indices, ratios of spectral irradiance, scaled band area and empirical orthogonal functions. The percentage of variance explained by these models ranged from 38 to 79%, with the best-performing approach being normalised difference indices. Given the low concentrations of integrated chl a observed in our study compared with previous studies, our statistical models performed surprisingly well in explaining variability in these concentrations. Our findings provide a basis for future work to develop methods for non-invasive time series measurements and medium- to large-scale spatial mapping of Antarctic ice algal biomass using instrumented underwater vehicles.

Identifying the full suite of processes that drive the melting of Antarctic sea ice each summer is crucial to improving the currently-poor ability of contemporary models to accurately simulate the climatological retreat phase of the annual sea-ice cycle. This is critical to (1) understanding and attributing observed trends and recent abrupt changes in sea-ice coverage and (2) the more robust prediction of future sea-ice conditions and impacts. This paper identifies wave-driven processes that can accelerate the seasonal melting of sea ice both in the marginal ice zone (MIZ) and in open-water areas within the interior sea-ice zone (SIZ). It builds on the long-held view that seasonal Antarctic sea-ice ablation is primarily driven by ice-floe lateral and basal melting enhanced in the MIZ by wave breakup of ice floes, by demonstrating that ocean waves play important additional roles in generating surface and interior melting (termed \"wave melting\") via three sets of processes: \"wave flooding\", \"wave pulverisation\", and \"wave greening\" (involving algal proliferation in wave-modified ice). Based on existing observations and simple one-dimensional modelling, these wave processes are estimated to reduce ice albedo by 0.38-0.64 compared to snow-covered ice, resulting in vertical melt-rate enhancements of 0.9-5.2 cm d.sup.-1 amplified by wave greening to 1.1-6.1 cm d.sup.-1 . The study also identifies five positive feedback and sub-feedback mechanisms that likely accelerate the ice melting further. It addresses a gap in current climate and Earth system models, which account for wave effects on floe-size distributions but overlook these coupled wave-driven dynamic, thermodynamic and biological processes that may contribute to explaining why and how Antarctic sea ice can melt back so rapidly each summer. An intention of this foundational study is to stimulate further targeted investigation aimed at quantifying the role of wave melting in the annual sea-ice cycle - as well as the contribution of wave greening to primary production in the sea-ice zone and its role in key biogeochemical processes that feed back to climate. The work has implications for planetary albedo, global climate feedbacks, marine ecosystems, and the accuracy of future sea-ice and climate projections in an increasingly-stormy Southern Ocean, as well as in a changing Arctic.

INTRODUCTION: With rising student debt, identifying ways for students to contain the cost of their education is highly desired. Numerous prerequisite courses are required for admission to a physical therapy program and have been shown to predict success in the National Physical Therapy Examination (NPTE) following graduation. Identifying how pre-admission courses completed at a 2-year vs 4-year institution impacts student success may allow students to be more selective about where they complete courses, thereby decreasing the amount of debt accumulated prior to entering graduate education. This study was designed to investigate the relationship between type of institution where students completed prerequisite coursework and subsequent NPTE scores and the related financial ramifications. METHODS: Participants (n=309) included students who graduated from two CAPTE-accredited DPT programs at private universities in the U. S. Midwest. This retrospective, correlational quantitative study analyzed independent variables that included GRE scores (verbal and quantitative), DPT GPA at the end of the first year, DPT GPA at graduation, undergraduate overall GPA and science GPA, number of credit hours completed at a 2-year institution, and number of prerequisite credit hours completed at a 2-year institution. Pearson correlation, multiple regression, and stepwise regression were utilized for data analysis. RESULTS:Multiple stepwise regression found that first-year DPT GPA alone was the most statistically significant predictor (r=0.591, p<0.001) of outcome on the NPTE, while GRE Quantitative improved the significance of the final predictive equation by 2.2%. Number of community college credit hours and prerequisite hours completed at a community college were not identified by multiple regression as predictors of variance in NPTE scores. CONCLUSION:With the first-year DPT GPA shown to explain 35% of the variance in NPTE scores, with an additional 2% contributed by GRE Quantitative, our findings can be used by faculty to identify students earlier who may need additional guidance and support. For students, taking prerequisite courses at a community college vs a 4-year institution is a cost-saving alternative found to have no impact on NPTE score.

Antarctic pack ice is inhabited by a diverse and active microbial community reliant on nutrients for growth. Seeking patterns and overlooked processes, we performed a large-scale compilation of macro-nutrient data (hereafter termed nutrients) in Antarctic pack ice (306 ice-cores collected from 19 research cruises). Dissolved inorganic nitrogen and silicic acid concentrations change with time, as expected from a seasonally productive ecosystem. In winter, salinity-normalized nitrate and silicic acid concentrations (C*) in sea ice are close to seawater concentrations (Cw), indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C* < Cw), commensurate with the seasonal build-up of ice microalgae promoted by increased insolation. Stronger and earlier nitrate than silicic acid consumption suggests that a significant fraction of the primary productivity in sea ice is sustained by flagellates. By both consuming and producing ammonium and nitrite, the microbial community maintains these nutrients at relatively low concentrations in spring. With the decrease in insolation beginning in late summer, dissolved inorganic nitrogen and silicic acid concentrations increase, indicating imbalance between their production (increasing or unchanged) and consumption (decreasing) in sea ice. Unlike the depleted concentrations of both nitrate and silicic acid from spring to summer, phosphate accumulates in sea ice (C* > Cw). The phosphate excess could be explained by a greater allocation to phosphorus-rich biomolecules during ice algal blooms coupled with convective loss of excess dissolved nitrogen, preferential remineralization of phosphorus, and/or phosphate adsorption onto metal-organic complexes. Ammonium also appears to be efficiently adsorbed onto organic matter, with likely consequences to nitrogen mobility and availability. This dataset supports the view that the sea ice microbial community is highly efficient at processing nutrients but with a dynamic quite different from that in oceanic surface waters calling for focused future investigations.

The temporal evolution of ice algae biomass, particulate and dissolved organic carbon (POC and DOC), and particulate and dissolved carbohydrates (pCHO and dCHO) was followed in land-fast, Arctic sea ice near Barrow, Alaska, USA. POC, DOC, pCHO, and dCHO were found in young ice before algal growth occurred, indicating initial allochthonous sources. In sediment-free ice, particulate organic pools (POC and pCHO) were more strongly related to ice algae biomass than the larger dissolved organic pools (DOC and dCHO). Although algae biomass peaked near the ice bottom, integrating across ice depth showed that most organic matter was found above the bottom layer. Sediment-containing ice held high organic matter concentrations, although peak ice algae biomass was lower than in sediment-free ice. Sediments incorporated in sea ice can be a source of allochthonous organic matter that is comparable to autochthonous contributions by ice algae. In late spring, much of the algae biomass in sediment-free ice was lost, in as little as 5 d. Nevertheless, large POC, DOC, pCHO, and dCHO pools remained in the ice, both near the bottom and in upper layers. Observations of natural ice cores melting in laboratory experiments demonstrated a network of extracellular polymeric substances (EPS) remaining attached to the ice bottom, even as the ice structure melted away. This retained EPS may partly explain the POC and carbohydrate pools found in sea ice after the loss of algae. Differential retention of organic matter by seasonal sea ice suggests that the characteristics of material exported from the ice will change as the melt season progresses.

Physical, biogeochemical and photosynthetic parameters were measured in sea ice brine and ice core bottom samples in the north-western Weddell Sea during early spring 2006. Sea ice brines collected from sackholes were characterised by cold temperatures (range -7.4 to -3.8°C), high salinities (range 61.4-118.0), and partly elevated dissolved oxygen concentrations (range 159-413 μmol kg⁻¹) when compared to surface seawater. Nitrate (range 0.5-76.3 μmol kg⁻¹), dissolved inorganic phosphate (range 0.2-7.0 μmol kg⁻¹) and silicic acid (range 74-285 μmol kg⁻¹) concentrations in sea ice brines were depleted when compared to surface seawater. In contrast, NH₄ ⁺ (range 0.3-23.0 μmol kg⁻¹) and dissolved organic carbon (range 140-707 μmol kg⁻¹) were enriched in the sea ice brines. Ice core bottom samples exhibited moderate temperatures and brine salinities, but high algal biomass (4.9-435.5 μg Chl a l⁻¹ brine) and silicic acid depletion. Pulse amplitude modulated fluorometry was used for the determination of the photosynthetic parameters F v/F m, α, rETRmax and E k. The maximum quantum yield of photosystem II, F v/F m, ranged from 0.101 to 0.500 (average 0.284 ± 0.132) and 0.235 to 0.595 (average 0.368 ± 0.127) in the sea ice internal and bottom communities, respectively. The fluorometric measurements indicated medium ice algal photosynthetic activity both in the internal and bottom communities of the sea ice. An observed lack of correlation between biogeochemical and photosynthetic parameters was most likely due to temporally and spatially decoupled physical and biological processes in the sea ice brine channel system, and was also influenced by the temporal and spatial resolution of applied sampling techniques.