Reply on RC2

This study investigates basin-scale tracer replacement timescales of the two polar oceans and the Atlantic, Indian, and Pacific Oceans using a one-degree global ocean-sea ice model that represents oceans under the largest Antarctic ice shelves, the Filchner-Ronne and Ross Ice Shelf (FRIS and RIS). After a long spin-up with present-day surface boundary conditions, we confirm that the model has a typical representation of wind-driven and thermohaline circulations in one-degree ocean models. We use virtual passive tracers placed in the five oceans and examine the behavior of the passive tracers to estimate the tracer replacement timescales and pathways of the basin-scale ocean waters. Replacement timescales in the polar oceans (114 years for the Southern Ocean and 109 years for the Arctic Ocean) are found to be shorter than those in the three oceans (217 years for the Atlantic Ocean, 163 years for the Indian Ocean, and 338 years for the Pacific Ocean). The Southern Ocean tracer has two clear pathways to the Northern Hemisphere: the surface route in the Atlantic Ocean and the bottom route in the Pacific and Indian Oceans. This surface route is a rapid conduit to transport the Southern Ocean signal to the North Atlantic and Arctic Oceans. The Atlantic Ocean tracer is transported to both polar regions along the North Atlantic Current and the Antarctic Circumpolar Current (ACC). The tracer experiments clearly demonstrate that Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in transporting the water masses in the Atlantic and Arctic Oceans to the Southern Ocean. The southward flow of the AMOC at the intermediate depths carries the northern waters to the ACC region, and then the water spreads over the Southern Ocean along the eastward-flowing ACC. The decay timescales of water in the ice-shelf cavities exposed to the water outside the Southern Ocean are estimated to be approximately 150 years for both the FIRS and RIS. The decay timescales in the Antarctic coastal region are short at the surface and long in the deep layers, with a noticeable reduction in the areas where ACC flows southward toward the Antarctic continent.

The Southern Ocean (SO) is one of the most pristine regions of our Planet, characterised by high levels of biodiversity (5% of the global diversity) (David and Saucède 2015) and hosting a unique fauna (up to 90% of SO species are endemic) (De Broyer and Danis 2011; Chown et al. 2015). Yet, the knowledge on SO biodiversity is still far from being completed. In addition, the knowledge on the impact that changing environments have on SO species-richness is very little and for some groups, it is still totally unknown. For instance, most of studies generally focus on one single species such as Antarctic krill (Kawaguchi et al. 2011), Clio pyramidata Linnaeus, 1767 (Orr et al. 2005), Globigerina bulloides d'Orbigny, 1826 (Moy et al. 2009), or only on a high taxonomic level (e.g. phylum, class): Echinodermata, Crustacea, Mollusca, Porifera, Bryozoa, Brachiopoda, Hydrozoa, Ascidiacea, Holoturoidea (Barnes 1999; Rowden et al. 2015; Post et al. 2017; Gutt et al. 2019; Vause et al. 2019; Pineda-Metz et al. 2020). Ultimately, the influence of sea-ice coverage on benthic species diversity was totally unknown prior to this study. In light of this, the objectives of the thesis are: 1. To expand the knowledge on shelf and deep-sea peracarid assemblage structure and abundance on a small regional (Weddell Sea) and on a large regional (Atlantic sector of the SO and South Atlantic Ocean) geographic scale. 2. To assess the environmental variables driving peracarid assemblage structure and abundance from the above mentioned areas. 3. To investigate SO benthic isopod species diversity from the Atlantic sector of the SO and assess the influence of environmental variables on their species-richness and composition. 4. To describe new possible peracarid species by means of integrative taxonomy, using morphological descriptions and whole genome sequencing analyses to support the species identification. Objective outcomes: The present thesis provides new information on the abundance and assemblage structure based on 64766 peracarid crustaceans from different 28 locations within the Atlantic sector of the SO continental shelf and deep sea (Chapters I-II). These locations are characterised by different environmental conditions, for instance different sea-ice concentrations. Results from Chapters I-II confirmed the dominance of peracarid assemblages in the benthos, with amphipods being the most abundant group, followed by isopods. Sea ice was identified as the main driver shaping benthic peracarid assemblage structure (Chapter I). On a larger geographic scale and wider bathymetric range (e.g. including sampling locations from previous studies performed in the South Atlantic Ocean and at a depth range from 160 to ~6000 m), depth was the main physical variable driving peracarid assemblage structure (Chapter III). In addition, 16157 isopod specimens from the Atlantic sector of the SO were identified to species level at a smaller scale (Chapter IV). In this case, sea ice was identified as the main physical driver affecting isopod diversity and composition among sampling locations (Chapter IV). Reduced concentration of sea ice causes a decrease in isopod biodiversity, thus climate change was identified as a huge threat for this taxon and for SO benthos in general. During the identification process, two new isopod species were discovered (Chapter V). The two new species (Notopais sp.1 n. sp. and Notopais sp.2 n. sp.) were accurately described and identified by means of integrative taxonomy. This provided the first whole genome sequencing of benthic isopods from the SO and the first complete mitochondrial genome of the genus Notopais (Chapter V). Thanks to the collaboration with the University of Genoa (Dipartimento di Scienze della Terra dell'Ambiente e della Vita, DISTAV, Italy) and the National Antarctic Museum (MNA) in Genoa, two new SO species of the suborder Valvifera G. O. Sars, 1883 were described by means of classical taxonomy. In this case, a molecular approach could not be used because both new species were represented by a single specimen, therefore it was important to preserve the integrity of the holotypes (Chapters VI-VII).

Carbon dioxide, temperature, salinity, and other variables collected via surface underway survey from Volunteer Observing Ship Marion Dufresne in the Indian Ocean, South Atlantic Ocean and Southern Oceans (> 60 degrees South) from 2007-01-04 to 2007-02-03 (NCEI Accession 0081000) (format: HTML)

<p class="abstracttextjpn entry-content">In this study, we investigate the wind-driven circulation in the Antarctic Ocean using a primitive two-layer model with realistic topography. A prominent feature of steady circulation driven by the annual mean wind stress is a clockwise(cyclonic) circulation in the lower layer at the Weddell Basin and the Australia Antarctic Basin. In particular, the circulation pattern in the Australia Antarctic Basin agrees with the observations. In these basins, negative vorticity input from the wind stress is transmitted to the lower layer through the diffusion term(Gent and McWilliams term) and causes prominent cyclonic gyres within closed geostrophic contours of f/H(f: Coriolis parameter, H: water depth). The model result forced by the seasonal wind stress shows that variations of the Antarctic Coastal Current are explained by wind stress variations along the coast. The transport of this current is determined by the integration of onshore Ekman transport along the coast. It is also shown that this Antarctic Coastal Current can be a part of the western boundary current in the Weddell Sea. On a time scale of 10 to 100 days, the variation of the upper layer thickness coincides with the sea level variation at Syowa Station. This variation might be attributed to coastal trapped waves driven by the alongshore wind stress.</p>

プリミティブ・モデルの定常解と準地衡風モデルの定常解、周期解を求める方法

An idealized climate change simulation is used to investigate the energetics of the Atlantic meridional overturning circulation (AMOC) at the stages of its weakening and recovery. There is a good correlation between the strength of the AMOC and the available potential energy (APE) in the upper 3 km of the ocean, integrated north of 50°N or globally, both during the weakening and recovery. Buoyancy forcing is important at both stages. In the Southern Ocean, the APE gradually builds up and correlates with the depth of pycnocline in the Atlantic Ocean. This suggests that mechanical forcing plays an important role in the recovery of the AMOC.

Most conceptual models of ocean circulation during past glacial periods invoke a shallowed North Atlantic‐sourced water mass overlying an expanded, poorly ventilated Southern Ocean (SO)‐sourced deep water mass (Southern Component Water or SCW), rich in remineralized carbon, within the Atlantic basin. However, the ventilation state, carbon inventory, and circulation pathway of SCW sourced in the Pacific sector of the SO (Pacific SO) during glacial periods are less well understood. Here we present multiproxy data—including δ18O and δ13C measured on the benthic and planktic foraminifera Cibicidoides wuellerstorfi, and Neogloboquadrina pachyderma, and productivity proxies including percent CaCO3, total organic carbon, and Ba/Ti—from a sediment core located in the high‐latitude (71°S) Pacific SO spanning the last 800 kyr. Typical glacial δ13C values of SCW at this core site are ~0‰. We find no evidence for SCW with extremely low δ13C values during glacials in the high‐latitude Pacific SO. This leads to a spatial gradient in the stable carbon isotope composition of SCW from the high‐latitude SO, suggesting that there are different processes of deep‐ and bottom‐water formation around Antarctica. A reduced imprint of air‐sea gas exchange is evident in the SCW formed in the Atlantic SO compared with the Pacific SO. A spatial δ13C gradient in SCW is apparent throughout much of the last 800,000 years, including interglacials. A SO‐wide depletion in benthic δ13C is observed in early MIS 16, coinciding with the lowest atmospheric pCO2 recorded in Antarctic ice cores.

The Atlantic Meridional Overturning Circulation (AMOC), crucial for transporting heat northward across the Atlantic Ocean, is expected to weaken due to global warming, with implications for global climate. It is uncertain, however, how much it will weaken or if it may even completely collapse this century. Hence, we assess the AMOC's ability to withstand extreme increases in greenhouse gases and freshwater forcing in the North Atlantic by examining the upwelling pathways that return deep waters of the AMOC to the surface in 34 CMIP6 climate models. Our findings show that upwelling in the Southern Ocean, maintained by persistent overlying westerly winds, prevents a total AMOC collapse and impacts its future strength. This Southern Ocean upwelling must be balanced by downwelling in the Atlantic or Pacific oceans, so only the development of a strong Pacific Meridional Overturning Circulation (PMOC) could enable an AMOC collapse. While a PMOC does appear in nearly all models, it is insufficient to offset the upwelling in the Southern Ocean, suggesting an AMOC collapse this century is unlikely. We uncover novel stabilising mechanisms that enhance the resilience of the AMOC, with implications for its past and future change. Our findings highlight the critical need for improved observation-based estimates of the Indo-Pacific and Southern Ocean circulations to reduce uncertainty in AMOC projections.

Distribution of perfluoroalkyl compounds in seawater from Northern Europe, Atlantic Ocean, and Southern Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 601:109-126 (2018) - DOI: https://doi.org/10.3354/meps12660 Traits structure copepod niches in the North Atlantic and Southern Ocean Niall McGinty1,2,*, Andrew D. Barton3, Nicholas R. Record4, Zoe V. Finkel1, Andrew J. Irwin2 1Environmental Science Program, Mount Allison University, Sackville, NB E4L 1E2, Canada 2Department of Mathematics and Computer Science, Mount Allison University, Sackville, NB E4L 1E2, Canada 3Scripps Institution of Oceanography and Section of Ecology, Behavior and Evolution, UC San Diego, CA 2093-0218, USA 4Bigelow Laboratory for Ocean Sciences, ME 04544, USA *Corresponding author: nmcginty@mta.ca ABSTRACT: Realised niches describe the environmental and biotic conditions that a species occupies. Among marine zooplankton, species traits, including body size, dietary mode (herbivore, omnivore, or carnivore), and diapause strategy are expected to influence the realised niche of a species. To date, realised niches are known for only a small number of copepod species. Here we quantify the realised niches of 88 copepod species measured by the Continuous Plankton Recorder (CPR) in the North Atlantic and Southern Ocean using Maximum Entropy (MaxEnt) modelling. We estimate the univariate mean niche, niche breadth of copepods for several important environmental variables, and assess the relative effects of several key zooplankton traits on the mean niche. Sea surface temperature (SST) contributed the most information to the description of niches on average across all species, with the rank importance of the remaining variables varying between regions. In the North Atlantic SST, depth, salinity and chlorophyll niches separated omnivores and herbivores from carnivores while in the Southern Ocean niche differences across dietary modes were found for chlorophyll and wind stress only. Diapausing copepods were found to occur in colder temperatures compared with non-diapausing taxa, likely because of their capacity for accumulating lipids. A strong negative body size-niche breadth relationship was found only for diapausing copepods, suggesting that larger multi-year generation species are more reliant on a specific temperature range to successfully reach diapause. Our analysis demonstrates strong connections between copepod traits and their realised niches in natural populations. KEY WORDS: Copepods · Niche · Diet · Body size · Diapause · MaxEnt · North Atlantic · Southern Ocean Full text in pdf format Supplementary material PreviousNextCite this article as: McGinty N, Barton AD, Record NR, Finkel ZV, Irwin AJ (2018) Traits structure copepod niches in the North Atlantic and Southern Ocean. Mar Ecol Prog Ser 601:109-126. https://doi.org/10.3354/meps12660 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 601. Online publication date: August 09, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Ichthyofauna of mesopelagial of high-latitude areas in the World Ocean is considered in the paper on the basis of taxonomic reports and revisions of recent years. Different degree of endemism of mesopelagic ichthyofauna in different high-latitude areas of the World Ocean is recorded. The South Ocean and the northern Pacific are characterized by the highest degree of endemism at generic and species levels. Hypothesis of the earliest (Oligocene-Miocene) time of formation of high-latitude ichthyofauna of the pelagial of the South Ocean is advanced. In the northern hemisphere, high-latitude areas of the northern Pacific are characterized by the earliest time of formation of pelagic ichthyofauna—presumably the Miocene-Pliocene. Ichthyofauna of the mesopelagial of the North Atlantic has the youngest age: Pliocene-Pleistocene. Bipolarity of high-latitude ichthyofauna of mesopelagial was considered. Maximum number of common (identical) pairs of species (14) inhabits the northern Atlantic and the South Ocean. The South Ocean and the northern Pacific are characterized by minimal number of common pairs of species (3). The remaining bipolar taxa are represented mainly by more or less closely related species of specific high-latitude genera, whose number in the South Ocean is greater than in the northern Atlantic and Pacific. On the basis of data of paleooceanology of the Cenozoic period, the hypothesis of formation of bipolar taxa and their ranges in connection with change in configuration of continents, oceans, and climate change is considered.

Abstract. Stable water isotopologues (SWIs) are useful tracers of moist diabatic processes in the atmospheric water cycle. They provide a framework to analyse moist processes on a range of timescales from large-scale moisture transport to cloud formation, precipitation and small-scale turbulent mixing. Laser spectrometric measurements on research vessels produce high-resolution time series of the variability of the water vapour isotopic composition in the marine boundary layer. In this study, we present a 5-month continuous time series of such ship-based measurements of δ2H and δ18O from the Antarctic Circumnavigation Expedition (ACE) in the Atlantic and the Southern Ocean in the time period from November 2016 to April 2017. We analyse the drivers of meridional SWI variations in the marine boundary layer across diverse climate zones in the Atlantic and Southern Ocean using Lagrangian moisture source diagnostics and relate vertical SWI differences to near-surface wind speed and ocean surface state. The median values of δ18O, δ2H and deuterium excess during ACE decrease continuously from low to high latitudes. These meridional SWI distributions reflect climatic conditions at the measurement and moisture source locations, such as air temperature, specific humidity and relative humidity with respect to sea surface temperature. The SWI variability at a given latitude is highest in the extratropics and polar regions with decreasing values equatorwards. This meridional distribution of SWI variability is explained by the variability in moisture source locations and its associated environmental conditions as well as transport processes. The westward-located moisture sources of water vapour in the extratropics are highly variable in extent and latitude due to the frequent passage of cyclones and thus widen the range of encountered SWI values in the marine boundary layer. Moisture loss during transport further contributes to the high SWI variability in the extratropics. In the subtropics and tropics, persistent anticyclones lead to well-confined narrow easterly moisture source regions, which is reflected in the weak SWI variability in these regions. Thus, the expected range of SWI signals at a given latitude strongly depends on the large-scale circulation. Furthermore, the ACE SWI time series recorded at 8.0 and 13.5 m above the ocean surface provide estimates of vertical SWI gradients in the lowermost marine boundary layer. On average, the vertical gradients with height found during ACE are -0.1‰m-1 for δ18O, -0.5‰m-1 for δ2H and 0.3 ‰ m−1 for deuterium excess. Careful calibration and post-processing of the SWI data and a detailed uncertainty analysis provide a solid basis for the presented gradients. Using sea spray concentrations and sea state conditions, we show that the vertical SWI gradients are particularly large during high wind speed conditions with increased contribution of sea spray evaporation or during low wind speed conditions due to weak vertical turbulent mixing. Although further SWI measurements at a higher vertical resolution are required to validate these findings, the simultaneous SWI measurements at several heights during ACE show the potential of SWIs as tracers for vertical mixing and sea spray evaporation in the lowermost marine boundary layer.

The Southern Ocean Meridional Overturning Circulation (MOC) has intensified in recent decades, yet the interplay between its Eulerian and eddy components under future warming remains uncertain. Using ensemble climate simulations, here we show that the Eulerian-mean MOC shifts poleward under high-emission scenarios during the twenty-first century, with compensating eddy-induced MOC sustaining a uniformly intensified residual overturning. This response is less pronounced under low-emission scenarios with climate mitigation. Likewise, a poleward-shifted Eulerian-mean MOC occurred during the Mid-Pliocene Warm Period, but with weaker, broader eddy compensation, leading to non-uniform intensified residual overturning. Across past and future warming climates, the eddy-induced MOC is primarily modulated by surface heat flux changes at lower latitudes and by freshwater flux changes at higher latitudes over the Southern Ocean. The buoyancy forcing changes drive northward Antarctic upwelling, promoting Antarctic bottom water formation. Along with MOC changes, ventilation intensifies in the lower latitudes of the Southern Ocean as related to the subduction branch, especially during the past warm period.

Here we consider the role of depth as a driver of evolution in a genus of deep-sea fishes. We provide a phylogeny for the genus Coryphaenoides (Gadiformes: Macrouridae) that represents the breadth of habitat use and distributions for these species. In our consensus phylogeny species found at abyssal depths (>4000m) form a well-supported lineage, which interestingly also includes two non-abyssal species, C. striaturus and C. murrayi, diverging from the basal node of that lineage. Biogeographic analyses suggest the genus may have originated in the Southern and Pacific Oceans where contemporary species diversity is highest. The abyssal lineage seems to have arisen secondarily and likely originated in the Southern/Pacific Oceans but diversification of this lineage occurred in the Northern Atlantic Ocean. All abyssal species are found in the North Atlantic with the exception of C. yaquinae in the North Pacific and C. filicauda in the Southern Ocean. Abyssal species tend to have broad depth ranges and wide distributions, indicating that the stability of the deep oceans and the ability to live across wide depths may promote population connectivity and facilitate large ranges. We also confirm that morphologically defined subgenera do not agree with our phylogeny and that the Giant grenadier (formerly Albatrossia pectoralis) belongs to Coryphaenoides, indicating that a taxonomic revision of the genus is needed. We discuss the implications of our findings for understanding the radiation and diversification of this genus, and the likely role of adaptation to the abyss.

High volume air samples taken onboard several research vessels in the Atlantic Ocean, the Southern Ocean, and the Baltic Sea as well as at one land-based site close to Hamburg, Germany, in 2007 and 2008 were analyzed for per- and polyfluorinated organic compounds (PFCs). A set of neutral, volatile PFCs such as fluorotelomer alcohols (FTOH) or perfluoroalkyl sulfonamides and ionic nonvolatile PFCs like perfluorinated carboxylates (PFCA) and sulfonates (PFSA) were collected on PUF/XAD-2/PUF cartridges and glass fiber filters and determined using GC-MS and HPLC-MS/MS. PFCs were detected in all air samples, even in Antarctic regions, and occurred predominantly in the gas phase. Total gas-phase concentrations of ship-based samples ranged from 4.5 pg m(-3) in the Southern Ocean to 335 pg m(-3) in European source regions. Concentrations of 8:2 FTOH, the analyte that was usually observed in highest concentrations, were between 1.8 and 130 pg m(-3). PFC concentrations decreased from continental regions toward marine regions and from Central Europe toward the Arctic and Antarctica. Southern hemispheric concentrations of individual PFCs were significantly lower than those of the northern hemisphere. On the basis of this data set, marine background PFC concentrations and atmospheric residence times were calculated. This study gives further evidence that volatile PFCs undergo atmospheric long-range transportto remote regions and may contribute to their contamination with persistent PFCA and PFSA.