Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsi shelf during summer

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment

Very slow embryonic and larval development in the Antarctic limpet Nacella polaris

Cold polar marine species have very slow embryonic and larval development rates. Antarctic echinoids, bivalve molluscs and brooding gastropods develop up to 12 times slower than temperate and tropical species, departing from Arrhenius relationships and outside the normal Q 10 of 2–3 associated with 10 °C reductions in biochemical reaction rates. The slowing of development at temperatures around 0 °C has been reported previously to be much greater than for other parts of the global marine temperature range. Here we spawned and reared embryos and larvae of the Antarctic limpet Nacella polaris at 0.6 °C to the post-torsional veliger stage. Spawned eggs were 221 µm in diameter. Development rates were three times slower than any previously reported for patellogastropod limpets, with first division at 2.5 h post-fertilisation, the gastrula stage being reached after 55 h, hatching occurring after 70–75 h and the trochophore stage being reached after around 100 h. The marked slowing of development around 0 °C matches that previously reported for other polar taxa. This supports the hypothesis that there is a cold marine physiological transition to markedly slower physiological rates at temperatures near 0 °C. The transition is especially apparent here for development, but has also been reported for growth, both of which involve significant protein synthesis

Assessing the extent of establishment of Undaria pinnatifida in Plymouth Sound Special Area of Conservation, UK

The north-west Pacific kelp, Undaria pinnatifida, was first discovered in Europe on the Mediterranean coast of France (1971) and introduced to Brittany for aquaculture (1983). In the north-east Atlantic, it occurs in Spain, France, the British Isles, Belgium and Holland. The first UK record was in the Hamble estuary (1994) and it was found off Plymouth in 2003. The UK distribution is presently restricted to the south of England and the northern Irish Sea. We assessed the distribution of U. pinnatifida and native kelps and their allies in Plymouth Sound (at 0 to +1 m relative to Chart Datum). Undaria pinnatifida was widespread along rocky shores, on other hard substrata and grew in the same areas as Saccharina latissima and Saccorhiza polyschides. Undaria pinnatifida was significantly more abundant on vertical substrata than on upward-facing hard substrata. It was almost as common as all of the other kelp species combined on vertical substrata but was outnumbered by native species on upward-facing substrata. Undaria pinnatifida has become the visually dominant macroalga in marinas and has spread to surrounding natural habitats in Plymouth Sound. The extent to which it will outcompete native kelps requires monitoring, especially in conservation areas

Tetrasporophytic bias coupled with heterozygote deficiency in Antarctic Plocamium sp. (Florideophyceae, Rhodophyta)

International audienceMeiosis and syngamy generate an alternation between two ploidy stages, but the timing of these two processes varies widely across taxa, thereby generating life cycle diversity. One hypothesis suggests that life cycles with long-lived haploid stages are correlated with selfing, asexual reproduction, or both. Though mostly studied in angiosperms, selfing and asexual reproduction are often associated with marginal habitats. Yet, in haploid-diploid macroalgae, these two reproductive modes have subtle but unique consequences whereby predictions from angiosperms may not apply. Along the western Antarctic Peninsula, there is a thriving macroalgal community, providing an opportunity to explore reproductive system variation in haploid-diploid macroalgae at high latitudes where endemism is common. Plocamium sp. is a widespread and abundant red macroalga observed within this ecosystem. We sampled 12 sites during the 2017 and 2018 field seasons and used 10 microsatellite loci to describe the reproductive system. Overall genotypic richness and evenness were high, suggesting sexual reproduction. Eight sites were dominated by tetrasporophytes, but there was strong heterozygote deficiency, suggesting intergametophytic selfing. We observed slight differences in the prevailing reproductive mode among sites, possibly due to local conditions (e.g., disturbance) that may contribute to site-specific variation. It remains to be determined whether high levels of selfing are characteristic of macroalgae more generally at high latitudes, due to the haploid-diploid life cycle, or both. Further investigations of algal life cycles will likely reveal the processes underlying the maintenance of sexual reproduction more broadly across eukaryotes, but more studies of natural populations are required

The Use of Photographic Color Information for High-Throughput Phenotyping of Pigment Composition in Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N.Norris & Fredericq

Pigment variation within and among algal species may have important ecological consequences because small changes in the concentration and composition of pigments can influence the photosynthetic efficiency and rate as well as the spectra of light utilized. Toward the goal of developing a rapid method for comparing pigment composition among algal thalli, we characterized the relationship between visual color information taken from photographs (e.g., red, green, and blue color values) and photopigment composition in the non-native red alga Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N.Norris & Fredericq. We used a set of 19 thalli, collected from across the known native and non-native range in the Northern Hemisphere, which exhibited substantial color variation at the time of field collection, and sustained this variation after being maintained in a common garden. We identified a set of ecologically interesting pigment traits that are readily predicted by color information, including chlorophyll a and phycobilin concentration. Finally, we demonstrated the repeatability of estimating color phenotypes from photographs of thalli taken under a range of light conditions in order to evaluate the utility of this approach for field studies. We suggest this method could be useful for the rapid, high-throughput phenotyping of photopigments in other red algae as well

Sustained year-round oceanographic measurements from Rothera Research Station, Antarctica, 1997–2017

Oceanographic changes adjacent to Antarctica have global climatic and ecological impacts. However, this is the most challenging place in the world to obtain marine data due to its remoteness and inhospitable nature, especially in winter. Here, we present more than 2000 Conductivity-Temperature-Depth (CTD) profiles and associated water sample data collected with (almost uniquely) full year-round coverage from the British Antarctic Survey Rothera Research Station at the west Antarctic Peninsula. Sampling is conducted from a small boat or a sled, depending on the sea ice conditions. When conditions allow, sampling is twice weekly in summer and weekly in winter, with profiling to nominally 500 m and with discrete water samples taken at 15 m water depth. Daily observations are made of the sea ice conditions in the area. This paper presents the first 20 years of data collection, 1997-2017. This time series represents a unique and valuable resource for investigations of the high-latitude ocean’s role in climate change, ocean/ice interactions, and marine biogeochemistry and carbon drawdown

Quasi-weekly, year-round oceanographic and ice measurements at the coastal Western Antarctic Peninsula from 1997 to 2018

CTD: until 2003, a Chelsea Instruments Aquapak was used, with sampling to 200m due to the depth rating. Since then an SBE19 and SBE19+ have been alternated between use on station and servicing in the UK. These have been calibrated during servicing and compared with an SBE911+ CTD on board R/V Laurence M. Gould on joint casts (SBE19 tied to frame) and samples analysed on a Guildline Autosal 8400B Laboratory Salinometer Ammonium: samples were measured on a Turner TD-700 fluorometer. Macronutrients: from 1998 to 2017, samples were analysed on QuAAtro39 segmented flow auto-analyser at NOCS https://www.southampton.ac.uk/oes/research/facilities/dissolved-inorganic-and-organic-nutrient.page . From 2017 to 2018, samples were analysed on a SEAL analytical AAIII segmented flow colorimetric auto-analyser (Woodward and Rees, 2001). Chlorophyll: samples were measured on a Turner AU-10 fluorometer. Oxygen isotopes: From 1998 to 2012, the delta-O-18 measurements were made with a SIRA 10 mass spectrometer plus Isoprep18 device. From 2012 to 2017, the delta-O-18 measurements were made with an Isoprime 100 mass spectrometer plus Aquaprep device.,Year-round measurements of the water column in Ryder Bay, Western Antarctic Peninsula have been collected by the Rothera Marine Assistant and associated researchers, starting in 1997 as part of the Rothera Oceanographic and Biological Time Series (RATS) to assess temporal variability in physical and biogeochemical oceanographic properties. The data were collected using instrumentation deployed from rigid inflatable boats, or through instrumentation deployed through holes cut in the sea ice when the bay is frozen over in winter. Data collected include profiles to about 500m depth with a conductivity-temperature-depth (CTD) system that produces measurements of temperature, salinity, fluorescence and photosynthetically-active radiation (PAR). Individual water samples are collected with a Niskin bottle from a standard 15m depth, with some samples also collected from the surface layer. These individual samples are analysed for size-fractionated chlorophyll, macronutrients (nitrate, nitrite, ammonium, orthophosphate and silicic acid), stable isotopes of oxygen in seawater, and some ancillary parameters. The bottle data have been quality controlled using international reference standards. Profiling and water sample collection occur with quasi-weekly frequency in summer and weekly in winter, but are weather and sea ice dependent. In addition, daily assessments of sea ice concentration and sea ice type are made from nearby Rothera Research Station by visual inspection, to aid interpretation of the ocean data collected. These data constitute one of the longest time series of ocean measurements in Antarctica, with near-unique systematic data collection in winter, within either polar circle. Data collection has been supported since 1997 by the Natural Environment Research Council (NERC) through core funding supplied to the British Antarctic Survey. Since 2017, it has been supported by NERC award &ldquo;National Capability - Polar Expertise Supporting UK Research&ldquo; (NE/R016038/1).,Profile instrumentation was collected with a self-logging conductivity-temperature-depth (CTD) profiler, deployed from a rigid inflatable boat (RIBs) or sea ice sled and lowered on a hand-turned winch using a Kevlar rope. RIBs departed/returned to nearby Rothera Research Station. During periods of fast-ice cover in winter, profiling was conducted through holes cut in the ice. Three sites were targeted - a primary site (in approximately 500m water depth), a secondary site, and a tertiary site (very close to Rothera). When the primary site was unreachable due to sea ice, the secondary site was occupied, and failing that an approximately 100m cast was carried out somewhere accessible. When weather or ice were prohibitive, no data/samples were collected and there is also a gap due to the CTD being lost to a fire in winter 2001. Data are downloaded upon return to Rothera Research Station. Water samples were collected with a Niskin bottle, closed with a messenger, and either processed in the laboratories at Rothera or stored for shipping back to the UK for analysis. Water samples for macronutrients were filtered and frozen at -20 &deg;C other than Ammonium, which is measured locally. Ammonium: NH4 was measured at Rothera Research Station typically within four hours of collection. From 1997 to 2005 ammonium measurements were carried out using the indophenol technique adapted to utilise dichloroisocyanurate as the chlorine donor and a modified UV incubation (Catalano, 1987). The measurements were calibrated by spiking of triplicate samples with 0.25 to 2.5 &micro;M NH4Cl (Clarke and Leakey, 1996). From 2005, ammonium measurements were carried out using ortho-phthaldialdehyde (OPA) and fluorometry (Holmes et al., 1999). Sample measurements were carried out in triplicate, and calibrated using standard addition comprising four concentrations, also in triplicate (Clarke et al., 2008). Other macronutrients: Nitrate (NO3), nitrite (NO2), orthophosphate (PO4) and silicic acid (Si(OH)4) were measured in the UK using a standard nutrient autoanalyser approach (Strickland and Parsons, 1968). From 1998 to 2017, the samples were measured at National Oceanography Centre, Southampton; from 2017 to 2018, the samples were measured at the Plymouth Marine Laboratory. Chlorophyll: Collected water samples were gently mixed by inversion, and triplicate samples (100 ml in summer and 500ml in winter) were filtered immediately on return to the research station by gravity through sequential 47 mm filters as follows: i) Microphytoplankton (&amp;gt;20 &micro;m nylon mesh), ii) Large nanophytoplankton (5 to 20 &micro;m membrane filter), iii) Small nanophytoplankton (2 to 5 &micro;m membrane filter) Picophytoplankton (0.2 to 2 &micro;m membrane filter). Pigments were extracted into chloroform/methanol (Wood, 1985) and measured by fluorometry before and after addition of two drops of 0.1N HCl under low light levels. Calibration is carried out twice a year using chlorophyll a standards, with samples diluted as required during strong phytoplankton blooms to reduce the range of values measured. The ratio of fluorescence before and after acidification is used to assess the reliability of the phaeopigement data. All data are reported as chlorophyll a (calculated as total chlorophyll minus phaeopigment; Clarke et al., 2008). Oxygen isotopes: Unfiltered samples were stored in capped and sealed glass bottles with rubber inserts and minimal head space, and stored in the dark at +4 &deg;C during transport to the UK (Meredith et al., 2008). The samples were measured for oxygen isotopes using the CO2 equilibration method for oxygen (Epstein and Mayeda, 1953) in triplicate (Natural Environment Research Council Isotope Geosciences Laboratory, Keyworth, UK).,Salinity (and therefore effectively Density) In polar waters, with temperatures below approximately 4 &deg;C, density profiles largely follow the shape of the salinity profile. This means that salinity checks can also include density profile checks and the dynamical unlikeliness of density overturns. There are a limited number of casts with significant density overturns. As these would make the profiles unstable (dense water above less dense water) then is almost all cases they can be ascribed to sensor problems. They can happen throughout a profile but are more common at the surface of bottom of the profile. They were filtered by looking for an overturn of &amp;gt;0.05 kg m3 and also by looking for unusually large deviations between different mixed layer depth calculations (including using the 10m depth as the reference value). Spikes are then identified and removed manually in salinity in the initial processing (rats_cnv2mat). This is usually between 1 and 7 metres of data, though some profiles are completely removed (including events 1495 and 1999), where pump problems make all data invalid. The precision of the salinity data is ensured by salinity samples being collected and by joint casts between the RATS CTD(s) and that on the R/V Laurence M Gould, with adjustments applied in initial processing. Temperature Temperature has little effect on density in the range encountered and is therefore free to vary both up and down with depth such that there is no way to ascribe a profile to be physically implausible. The temperature data has been very robust, with no suspicious profiles and very tight matches in all joint casts, it is therefore presented as recorded, except for profiles with pump profiles, where the temperature looks less wrong than salinity but the depth the data is recorded at could be significantly different to the depth the water actually was when it entered the CTD. PAR From 2017 there have been repeating problems with the PAR sensors, despite servicing and changing sensors. Some values at depth are easily filtered as impossible but other times the values are within bounds, but the shape of the profile is unlikely. There are standard sampling issues, caused by the shade of the boat, ice and clouds, that means light can increase rapidly with time and/or depth. This makes filtering the problem profiles harder, without removing data where the sensor is working well. Often the shape of the profile is more important than the absolute values so these profiles that increase with depth are of reduced value. The first filtering is to use a mask created from the first 700 events and also remove values </span