Oceanic Regimes Research Articles

Ocean warming as a trigger for irreversible retreat of the Antarctic ice sheet

AbstractWarmer ocean conditions could impact future ice loss from Antarctica due to their ability to thin and reduce the buttressing of laterally confined ice shelves. Previous studies highlight the potential for a cold to warm ocean regime shift within the sub-shelf cavities of the two largest Antarctic ice shelves—the Filchner–Ronne and Ross. However, how this impacts upstream ice flow and mass loss has not been quantified. Here using an ice sheet model and an ensemble of ocean-circulation model sub-shelf melt rates, we show that transition to a warm state in those ice shelf cavities leads to a destabilization and irreversible grounding line retreat in some locations. Once this ocean shift takes place, ice loss from the Filchner–Ronne and Ross catchments is greatly accelerated, and conditions begin to resemble those of the present-day Amundsen Sea sector—responsible for most current observed Antarctic ice loss—where this thermal shift has already occurred.

Decoding drivers of carbon flux attenuation in the oceanic biological pump

The biological pump supplies carbon to the oceans’ interior, driving long-term carbon sequestration and providing energy for deep-sea ecosystems1,2. Its efficiency is set by transformations of newly formed particles in the euphotic zone, followed by vertical flux attenuation via mesopelagic processes3. Depth attenuation of the particulate organic carbon (POC) flux is modulated by multiple processes involving zooplankton and/or microbes4,5. Nevertheless, it continues to be mainly parameterized using an empirically derived relationship, the ‘Martin curve’6. The derived power-law exponent is the standard metric used to compare flux attenuation patterns across oceanic provinces7,8. Here we present in situ experimental findings from C-RESPIRE9, a dual particle interceptor and incubator deployed at multiple mesopelagic depths, measuring microbially mediated POC flux attenuation. We find that across six contrasting oceanic regimes, representing a 30-fold range in POC flux, degradation by particle-attached microbes comprised 7–29 per cent of flux attenuation, implying a more influential role for zooplankton in flux attenuation. Microbial remineralization, normalized to POC flux, ranged by 20-fold across sites and depths, with the lowest rates at high POC fluxes. Vertical trends, of up to threefold changes, were linked to strong temperature gradients at low-latitude sites. In contrast, temperature played a lesser role at mid- and high-latitude sites, where vertical trends may be set jointly by particle biochemistry, fragmentation and microbial ecophysiology. This deconstruction of the Martin curve reveals the underpinning mechanisms that drive microbially mediated POC flux attenuation across oceanic provinces.

Evidence of fin whale (Balaenoptera physalus velifera) recovery in the Canadian Pacific

Pacific fin whales (Balaenoptera physalus velifera), once the most abundant cetacean species in British Columbia (BC), were also one of the most heavily targeted by commercial whaling. Much of what we know about their phenology and ecology is from catch records, but their current status has not yet been summarized in Canadian waters. Here, we collated evidence from dedicated surveys, opportunistic sightings, and passive acoustic records that had not been reported before and reviewed them in the context of past data. This was to add new findings to what is known, and to establish if the population was showing signs of recovery. This is particularly relevant considering discussions of downlisting their population status in Canada from endangered to threatened. We then asked if this rebounding was consistent with what is known about pre-whaling presence and movement patterns, or if changes in whale distribution reflected altered oceanic regimes, prey availability, or increased anthropogenic pressures. The evidence suggested that fin whale populations in the northeast Pacific Ocean are repopulating areas along the BC coast recognized as part of their historic range. However, they are recovering in a different ocean than they were removed from, which makes them increasingly vulnerable to new anthropogenic threats. The sightings data suggested that, at least for the west coast of Vancouver Island, this repopulation has occurred over a relatively short period, with fin whales still absent from regular surveys as recent as the early 2000’s. The recent acoustic recordings suggested their presence is not transitory, but that fin whales may be using locales along the BC coast for feeding and breeding activities.

Improving the Statistical Representation of Tropical Cyclone In-Storm Sea Surface Temperature Cooling

Abstract This study uses fixed buoy time series to create an algorithm for sea surface temperature (SST) cooling underneath a tropical cyclone (TC) inner core. To build predictive equations, SST cooling is first related to single variable predictors such as the SST before storm arrival, ocean heat content (OHC), mixed layer depth, sea surface salinity and stratification, storm intensity, storm translation speed, and latitude. Of all the single variable predictors, initial SST before storm arrival explains the greatest amount of variance for the change in SST during storm passage. Using a combination of predictors, we created nonlinear predictive equations for SST cooling. In general, the best predictive equations have four predictors and are built with knowledge about the prestorm ocean structure (e.g., OHC), storm intensity (e.g., minimum sea level pressure), initial SST values before storm arrival, and latitude. The best-performing SST cooling equations are broken up into two ocean regimes: when the ocean heat content is less than 60 kJ cm−2 (greater spread in SST cooling values) and when the ocean heat content is greater than 60 kJ cm−2 (SST cooling is always less than 2°C), which demonstrates the importance of the prestorm oceanic thermal structure on the in-storm SST value. The new equations are compared to what is currently used in a statistical–dynamical model. Overall, since the ocean providing the latent heat and sensible heat fluxes necessary for TC intensification, the results highlight the importance for consistently obtaining accurate in-storm upper-oceanic thermal structure for accurate TC intensity forecasts. Significance Statement The ocean provides the heat and moisture necessary for tropical cyclone (TC) intensification. Since the heat and moisture transfer depend on the sea surface temperature (SST), we create statistical equations for the prediction of SST underneath the storm. The variables we use combine the initial SST before the storm arrives, the upper-ocean thermal structure, and the strength and translation speed of the storm. The predictive equations for SST are evaluated for how well they improve TC intensity forecasts. The best-performing equations can be used for prediction in operational statistical models, which can aid intensity forecasts.

Sustainable transformation of global ocean governance: Can a global public goods approach lead the way?

The 2030 Agenda for Sustainable Development (2030 Agenda), by setting integrated ocean goals (IOGs), is expected to strengthen the means of implementation of the legal regime of the 1982 Convention on the Law of the Sea (UNCLOS). This could lead to a sustainable transformation of global ocean governance in the Anthropocene to address systemic risks to the global oceans. Based on the realization of blue justice, the sustainable transformation of global ocean governance encompasses three holistic and interconnected dimensions: blue security, blue economy, and blue protection. It is a complex and adaptive global collective action that involves various actors and methodologies. This study introduces the concept of global public goods (GPGs) to the debate on sustainable transformation of global ocean governance, emphasizing that the process and outcome of governance transformation benefit mankind as a whole. Using cost-benefit analysis, aggregator techniques, and a heterogeneity game model to analyze the undersupply of GPGs, this study then argues that a framework for the provision of GPGs can provide adaptive institutional arrangements for coordinating the "collective action dilemma" involved in the sustainable transformation of global ocean governance. Collective action should be strengthened to promote the achievement of the SDGs: ⅰ) the establishment of international ocean regime complexity to facilitate coordination; ⅱ) the broad implementation of transboundary marine spatial planning as a tool for the coordination of interests; and ⅲ）the promotion of equitable capacity-building, including co-production of ocean knowledge, sharing information on marine data, and diversified financial support mechanisms to reduce heterogeneity.

Global Ocean pCO2 Variation Regimes: Spatial Patterns and the Emergence of a Hybrid Regime

AbstractThe variability in ocean surface partial pressure of carbon dioxide (pCO2), driven by both physical and biological processes, substantially influences air‐sea carbon exchange. It is widely recognized that the pCO2 variation at a specific ocean location is primarily dominated by either thermal or nonthermal effects. However, the distinct pCO2 variation regimes, their global distribution, and the mechanisms underlying such patterns have yet to be fully determined due to a paucity of global observations. Through the use of observation‐based products and an eddy‐resolving ocean simulation, this study demonstrates the presence of three distinct regimes in the global ocean: one in which sea surface temperature (SST) is the dominant control on pCO2 variations; another in which dissolved inorganic carbon (DIC) is the primary control; and a third previously uncharacterized hybrid regime where pCO2 variations are governed by seasonally‐varying factors. This hybrid regime is generally located between SST‐ and DIC‐dominated regimes and occupies approximately 15% of the global ocean. The regimes broadly exist in zonal bands that are closely linked to the relative strengths of SST and DIC variances. Seasonally‐varying mixed‐layer depth, mesoscale variability (quantified in terms of eddy kinetic energy), and biological processes modulate local pCO2 variations and play significant roles in shaping the global pattern of regime distributions. Understanding the distribution of pCO2 regimes, including the hybrid regime revealed in this study, as well as their different oceanic drivers, is essential for future predictions of ocean carbon uptake in response to global warming.

Resolution of the Tetrabothrius jagerskioeldi Cryptic Species Complex among Holarctic Alcidae (Charadriiformes): Cestodes among Fraterculinae—Exploring Marine Diversity, Host Range, and Dynamic Oceanography in the Greater North Pacific

In the biosphere, limits for diversity among species, communities, and biomes are revealed through intensive and extensive field-based inventory and assembly of voucher specimens and associated informatics examined in a phylogenetic, historical, ecological, and biogeographic arena. Archival resources for specimens and information contribute to a cumulative view of faunal structure and assembly under a comparative umbrella. Ultimately, species definitions, and inclusive partitions among populations and lineages, are fundamental in articulating hypotheses that examine interactions about evolution, the nature of organisms, and the condition of environments across space and time. We conclude our proposals establishing species limits for tapeworms of the cryptic complex historically accommodated in Tetrabothrius jagerskioeldi Nybelin, 1916 among Alcidae seabirds (Charadriiformes). Explorations of this facet of marine diversity summarize inventory data for species of Tetrabothrius Rudolphi, 1819 from field collections among 1,976 seabirds of 41 species representing 3 avian orders (Charadriiformes, Suliformes, Procellariiformes) examined across 58 oceanic/geographic localities from the greater North Pacific basin between 1949 and 2019, or over the past 70 years. Cestodes of the complex including T. jagerskioeldi sensu stricto, T. alcae Hoberg and Soudachanh, 2021, and T. sinistralis Hoberg and Soudachanh, 2021, along with 2 previously unrecognized taxa, are documented, occurring in 128 of 1976 seabirds examined (6%) and 17 of 41 marine avian species from 23 insular, coastal, and pelagic sites spanning the North Pacific. In completing an evaluation of this assemblage, we focus on those cestodes among 8 species of medium- to small-bodied alcids, subfamily Fraterculinae. Specimens designated as Tetrabothrius fraterculus n. sp. were observed among puffins (2 species of Fraterculus and Cerorhinca), whereas Tetrabothrius aithuia n. sp. is proposed for tapeworms in auklets (4 species of Aethia and Ptychoramphus) and a puffin (Cerorhinca); both cestodes are currently unknown among the Alcinae species of Cepphus, Uria, Brachyramphus, and Synthliboramphus based on the North Pacific inventory collections. These large-bodied cestodes, typical of the 5 species in the complex, are characterized among 46 currently valid species of Tetrabothrius in avian hosts, based on unique configurations of the genital atrium; male and female genital papillae; terminal genital ducts; numbers of testes; and the structure, position, and dimensions of the vaginal and atrial seminal receptacles. Ancillary characters contributing to differentiation include attributes of the scolex, structure, dimensions, and position of the vitelline gland and relative position of the dorsal and ventral osmoregulatory canals. A suite of complex attributes unequivocally separates 5 respective species that had historically been relegated to a single geographically widespread and morphologically variable taxon under T. jagerskioeldi sensu lato. Host range for respective cryptic species of the T. jagerskioeldi–complex reveal an intricate view of ecological isolation and connectivity across the greater North Pacific basin. Seabirds, marine mammals, and parasites are indicators of changing conditions over space and time. Oceanic regime shifts, prey cascades, and diversity for birds and parasites serve as proxies for revealing accelerating perturbation in marine foodwebs under climate forcing.

Oceanic Regime Shift to a Warmer Continental Shelf Adjacent to the Shackleton Ice Shelf, East Antarctica

AbstractThe long‐held view that the East Antarctic margin is isolated from warm offshore waters has been challenged by recent observations showing incursions of warm modified Circumpolar Deep Water (mCDW) reaching several East Antarctic ice shelves. However, large areas of the East Antarctic continental shelf remain poorly observed, making it challenging to determine if the supply of oceanic heat to the ice shelves is changing. Here, we use temperature and salinity profiles to the west of the Shackleton Ice Shelf (SIS; ≈100°E) spanning 60 years to assess the variability of the water masses in the context of a changing climate. We document warming and freshening of shelf waters. Prior to 1996, cold mCDW water (θ < −1.6°C) was found below the surface mixed layer and cold Dense Shelf Water (DSW) with a salinity of >34.5 dominated the water column. After 2010, warm mCDW (≥−1.0°C) was widespread over the continental shelf and DSW with salinity over 34.5 was no longer present. The mixing ratio of glacial meltwater indicates that warm mCDW observed in 2011 caused basal melting of the SIS, possibly reducing the salinity of DSW. Increased access of warm waters to the continental shelf may have also occurred on the eastern side of the ice shelf, where glaciological evidence shows the grounding line has retreated. These observations suggest a shift occurred prior to 2011 that has increased the ocean heat supply to the continental shelf and to the SIS, increasing basal melt and reducing DSW formation.

Atmospheric CO2 Isotopic Variations, with Estimation of Ocean and Plant Source Contributions

This analysis uses both atmospheric CO2 concentrations and the accompanying δ13C isotopic measurements of CO2 over 40 years from 1978 to 2015 observed at ten different latitudes from 90° S to 82 °N. Atmospheric CO2 is separated into two components of CO2 attributable to deep ocean and to plant (including fossil fuel) sources. The isotopic values assigned to the two components are δ13C = 0‰ and −26‰, respectively. The latitude variations in residual source component CO2 show the ocean source component peaking at the equator. This contrasts with the residual plant source component that peaks in the Arctic Circle region. Seasonal comparisons show no change in the ocean component peaking at the equator and no significant changes in its variation with latitude, while the plant component shows seasonal changes of the order of 15 ppm at high latitudes. The ocean component shows clear anomalous behavior in the three years following the 1989 Pacific Ocean regime shift (a shift independently identified from the changed biological time series). By contrast, the residual plant component shows a correlation in the timing of maxima in its annual variations with the timing of El Nino events over the time span of 1985–2015. It also shows a discontinuity in annual variation coinciding with the 1995 AMO phase change. We conclude that the ocean and plant components of atmospheric CO2 relate to independent sources of atmospheric CO2 and have approximately equal magnitudes. The observations are consistent with a hypothesis that variations in the ocean components have an origin from upwelling water from deep ocean currents, and variations in plant components are dominated by a combination of fossil fuel CO2, phytoplankton productivity, and forest and peat fires, which primarily occur in the northern hemisphere.

Exploring late Pleistocene bioturbation on Yermak Plateau to assess sea-ice conditions and primary productivity through the Ethological Ichno Quotient

Central Arctic, interglacial intervals have traditionally been associated with diverse and intense bioturbation, and abundant foraminifera, interpreted as indicating relatively low sea-ice concentrations and productive surface waters, while glacial intervals, typically barren, support the inverse. In this respect, the Yermak Plateau is anomalous. Biomarker studies suggest that glacial intervals were characterized by comparatively open water, while interglacials are marked by severe sea-ice conditions. Here we study downcore Ethological Ichno Quotient (EIQ) variations in trace fossils and bioturbation to test the hypothesis that different ethological classes vary in accordance with late Pleistocene changes in sea-ice extent, with deposit feeders increasing during reduced sea-ice cover and chemosymbiotic traces increasing during periods of thick perennial sea-ice conditions. Our results generally demonstrate that the abundance of traces like Planolites, Scolicia, and burrows produced by deposit feeders increase during episodes of seasonal sea-ice cover. In contrast, intervals with more severe sea-ice conditions are characterized by chemosymbiotic traces such as Chondrites and Trichichnus/Mycellia, suggesting lower food delivery and poorly ventilated bottom water conditions. The study thus confirms previous reconstructions of sea-ice conditions on the Yermak Plateau during interglacials, demonstrating that bioturbation variation provides insights into bentho-pelagic coupling under variable sea ice regimes in the Arctic Ocean.

The effects of the Patagonian shelf-break front on copepod abundance, biodiversity, and assemblages

Fronts play an important role in ecological processes, having multiple effects on the structure of plankton communities. The Argentine Sea is characterized by the presence of the large and very productive Patagonian shelf-break front (PSBF). This is a permanent front, with high thermohaline gradients defined between the relatively warmer and fresher shelf waters and those of the Malvinas Current. We studied the effects of the PSBF in the vertical and horizontal structure of the copepod community along two transects crossing the front. For all the variables studied, the outer shelf plus the front behaves as a unity, different of the offshore oceanic region. The highest copepod abundances were recorded on the outer shelf and shelf-break front, while the highest diversity was verified in the oceanic regime. Three copepod assemblages were identified associated to different regions: outer shelf and front (OS-PSBF), upper (UMW) and deeper (DMW) Malvinas waters, each one characterized by its own set of indicator species, having different reproductive and feeding strategies. Sac-spawners, ambush or cruise-feeders, and detritivore or omnivore species, occurred in DMW, while broadcasters, filter-feeders and mainly herbivores dominated at UMW and OS-PSBF. The PSBF acts as a leaky boundary between the oceanic regime (UMW and DMW) and the outer shelf-front regime (OS-PSBF), the first one characterized by higher copepod diversity and several functional groups, and the last one depicted by higher copepod abundance and only one functional group. In addition to its high primary production, the PSBF and surroundings are important to provide diversity of pelagic habitats that promote the existence of different assemblages, which are characterized by species having similar functional traits and that could play a similar role in the ecosystem.

Increased warm water intrusions could cause mass loss in East Antarctica during the next 200 years

The East Antarctic Ice Sheet (EAIS) is currently surrounded by relatively cool water, but climatic shifts have the potential to increase basal melting via intrusions of warm modified Circumpolar Deep Water (mCDW) onto the continental shelf. Here we use an ice sheet model to show that under the current ocean regime, with only limited intrusions of mCDW, the EAIS will likely gain mass over the next 200 years due to the increased precipitation from a warming atmosphere outweighing increased ice discharge due to ice-shelf melting. However, if the ocean regime were to become dominated by greater mCDW intrusions, the EAIS would have a negative mass balance, contributing up to 48 mm of SLE over this time period. Our modelling finds George V Land to be particularly at risk to increased ocean induced melting. With warmer oceans, we also find that a mid range RCP4.5 emissions scenario is likely to result in a more negative mass balance than a high RCP8.5 emissions scenario, as the relative difference between increased precipitation due to a warming atmosphere and increased ice discharge due to a warming ocean is more negative in the mid range RCP4.5 emission scenario.

The ebb and flow of the Seaflower marine biosphere reserve: Law entanglements and socio‐environmental justice in the southwestern Caribbean Sea

AbstractThis paper explores the spatio‐legal dynamics of marine protected areas and their relation to socio‐environmental justice. It adopts a critical legal geography perspective to unpack ocean lawscape configurations triggered by territorial claims, the international mechanisms for maritime boundary‐making, and state sovereignty instruments. It is empirically focused on the Seaflower marine biosphere reserve, a protected area amid a geopolitical contestation between Nicaragua and Colombia in the southwestern Caribbean. By analysing its spatio‐legal history over two decades (2000–2021), the paper sheds light on the marine legalities of this region, which are often contradictory and overlapping. Focusing on the marine lawscape of Colombia, it explores the relationship between protected areas and marine territorialisation, also reflecting on the governance regimes' effects on indigenous livelihoods and marine biodiversity. The paper concludes that (i) marine protected areas are regularly being disrupted, re‐bordered, and reconfigured by the international ocean regimes governing the oceans; (ii) the link between the creation and management of marine protected areas and territorial jurisdiction compromises social and environmental justice, and (iii) inclusion of indigenous legalities might enhance equity and sustainability in ocean governance.

Determination of dissolved organic carbon and total dissolved nitrogen in seawater using High Temperature Combustion Analysis

This document describes best practices for analysis of dissolved organic matter (dissolved organic carbon and total dissolved nitrogen) in seawater samples. Included are SOPs for sample collection and storage, details for laboratory analysis using high temperature combustion analysis on Shimadzu TOC analyzers, and suggestions for best practices in quality control and quality assurance. Although written specifically for GO-SHIP oceanographic community practices, many aspects of sample collection and processing are relevant to DOM determination across oceanic regimes and this document aims to provide updated methodology to the wider marine community.

Birth and Decline of Magma Oceans in Planetesimals: 2. Structure and Thermal History of Early Accreted Small Planetary Bodies

AbstractThis is the second of two companion papers that present a theoretical and experimental study of the thermal history of planetesimals in which heating by short‐lived radioactive isotopes generates an internal magma ocean and the subsequent cooling and crystallization thereof. We study the conditions required to form and preserve basal cumulates and flotation crusts, and the implications for the thermal evolution of planetary bodies. Our model predicts that planetesimals larger than 30 km can reach 1300°C and a melt fraction of 40 vol%, producing a solid‐like to liquid‐like rheological transition that triggers an internal magma ocean. In the magma ocean regime core‐mantle differentiation occurs very quickly and the mantle convects under a relic of chondritic material whose thickness is controlled by the temperature of rheological transition. We show that the magma ocean episode is associated with time‐dependent crystal segregation and no re‐entrainment. Segregation of crystals is essentially constrained by their size and by their density difference with respect to the melt, the latter being fully determined by the planetesimal's initial composition. Olivine cumulates are likely to form at the core‐mantle boundary. Under certain particular conditions, a flotation crust can also form, which reduces the efficiency of heat evacuation by convection, thereby enhancing the magma ocean's lifetime and the efficiency of crystal segregation. Two types of large‐scale mantle structure are possible outcomes: a well‐mixed upper mantle above an olivine cumulate, or a more finely layered “onion‐shell” structure.

Multiscale distribution patterns of pelagic rafts of sargasso (Sargassum spp.) in the Mexican Caribbean (2014–2020)

As the biomass of pelagic Sargassum spp. increased across the North Atlantic equatorial recirculation region from 2011 onwards, massive rafts of sargasso appeared in the Western Caribbean in 2015, 2018, 2019, and 2020. These events raised concerns regarding their negative consequences on the environment, local income, and human wellbeing. As adequate monitoring and analysis tools are needed for designing in-water and on-beach control strategies to reduce potential negative impacts, more robust and spatially explicit information is needed in order to improve sargasso management and focus restoration efforts. In this paper, we offer a spatiotemporal multiscale description of sargasso distribution and dynamics for 2014–2020 in the Mexican Caribbean: (1) for the entire region (millions of km2); (2) at the local scale (thousands of km2) evaluating the dynamics inside the reef lagoon at Puerto Morelos, Mexico; and finally, (3) specific beach observations (hundreds of km2) derived from data on beach cleaning volumes. Fifteen areas in the Mexican Caribbean, with different sargasso dispersions and on-shore accumulations, were evaluated. The areas around Tulum, Solidaridad, and Puerto Morelos have the most extreme and most frequent episodes but also exhibited the greatest seasonal variability. Extreme sargasso presence can occur in the Western Caribbean in any season, albeit with increasing coverage and recurrence in the summer. Images from a coastal video monitoring station at Puerto Morelos showed that massive sargasso beaching was associated with low energy conditions (Hs< 0.25 m, wind speed<4 m/s, neap tide), while non-accumulation of sargasso on the beach occurred under high energy conditions (Hs >0.4 m, wind speed = 8 m/s, spring tide). Time-series analyses of sargasso beaching showed different periods of historic maximum sargasso coverage over July–October 2018 and others in January–February 2019. Wind and wave regimes influenced sargasso in distinct ways, depending on the coastal section, probably related to coastline morphology, oceanic regime, or the extent of the continental platform. This work presents the longest systematic time series (2014-2020) of high resolution satellite detected sargasso in Mexico. Spatial and temporal patterns are proposed as fundamental steps for managing sargasso accumulations.

Changes in Arctic Halocline Waters Along the East Siberian Slope and in the Makarov Basin From 2007 to 2020

AbstractThe evolution of halocline waters in the Makarov Basin and along the East Siberian continental slope is examined by combining drifting platform observations, shipborne hydrographic data, and simulations from a global operational physical model from 2007 to 2020. From 2012 onwards, relatively shallow and cold Atlantic‐derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian continental slope. Their eastward extent abruptly shifted from 155°E to 170°E in early 2012, stabilized at 170°E until the end of 2015, then gradually advanced to reach the western Chukchi Sea in 2017. Such eastward progression led to a strengthening of the associated boundary current and to the shedding of mesoscale eddies of cold Atlantic‐derived waters into the lower halocline of the Makarov Basin in September 2015 and near the East Siberian continental slope in November 2017. Additionally, active mixing between upwelled Atlantic Water and shelf water formed dense warm water supplying the Makarov Basin lower halocline. The increasing contribution from Atlantic‐derived waters into the lower halocline along the East Siberian continental slope and in the Makarov Basin led to a weakening of the halocline, which is characteristic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime may now extend toward the Amerasian Basin.

Seasonal and decadal variations in absorption properties of phytoplankton and non-algal particulate matter in three oceanic regimes of the Northwest Atlantic

Seasonal and inter-annual absorption properties of phytoplankton and non-algal particulate matter were studied in relation to phytoplankton biomass, as indexed by chlorophyll-a concentration, and presence of diatoms, as indexed by fucoxanthin concentration, using a 20-year time series of in situ data collected in the Northwest Atlantic. We found significant differences in the spatiotemporal variations of the bio-optical properties for three oceanic regimes: mesotrophic (Scotian Shelf), oligotrophic (Northwest Atlantic Basin, NAB), and subartic (Labrador Sea). The Scotian Shelf and NAB exhibited similar phenology with the spring and autumn blooms associated with low phytoplankton specific absorption, while only relatively high fucoxanthin concentration occurred in spring. The NAB showed a smaller seasonal variation than the Scotian Shelf in agreement with its oceanic conditions. The Labrador Sea showed a single phytoplankton bloom in spring followed by a continuous decrease in biomass the rest of the year. The relationship between phytoplankton absorption coefficient at 443 nm and chlorophyll-a concentration was consistent with other studies with coefficients that were region-dependent. Absorption by non-algal particulate matter remained between 5% and 60% of phytoplankton absorption with a mean of 15%. The slope of the non-algal particulate absorption varied with seasons and regions and appeared to depend on the trophic status with high values (i.e., up to 0.04) occurring during bloom conditions. We also introduced a new index, the phytoplankton apparent absorption wavelength (PAAW), a wavelength-weighted sum of absorption expressed in nanometers that provides information on the phytoplankton biomass and assemblage in a simple manner. Time series analysis of the PAAW revealed a decrease of this property in spring on the Scotian Shelf, NAB, and Labrador Sea and an increase in autumn on the Scotian Shelf and NAB, suggesting a shift in these ecosystems.

Long-term hydrographic changes in the Gulf of California and ecological impacts: A crack in the World’s Aquarium?

Although the Gulf of California is widely recognized as a region of high productivity and biodiversity, recent oceanographic and ecological changes have had a significant impact on its overall health. We review the relevant history of the economically important fishery based on large Humboldt (jumbo flying) squid (Dosidicus gigas) (>50 cm mantle-length and 10 kg body weight) that existed in the Guaymas Basin from the 1990′s until 2009, when a strong El Niño was accompanied by precocious spawning of squid at extremely small size (<30 cm mantle length and 0.1 kg). This short-lived phenotype is characteristic of the equatorial part of the species range and cannot be profitably fished. This phenomenon also occurred in conjunction with the strong 1997–1998 El Niño. Although rapid recovery of squid size and landings occurred after the 1997–1998 event, recovery after 2009–2010 El Niño was still incomplete when another strong El Niño occurred in 2015–2016. This last event has led to fixation of the small size-at-maturity phenotype in the Gulf of California — an effective poleward migration of the tropical phenotype. We also document years between El Niño 2009–2010 and 2015–2016 as being characterized by significant subsurface warming, leading to decreased productivity and restricted nighttime foraging opportunities for squid in the upper water column. These climatic trends have likely altered trophic webs throughout the Gulf of California, impacting many other taxa, including small pelagic fishes that are ecologically vital and commercially harvested in large quantities, as well as a suite of larger teleost fishes that are targeted by sport fishers. From these disparate data sources, collected and collated in coordination with regional resource users and environmental monitoring programs, an overall pattern emerges of long-term decline across multiple taxa. We also present evidence of a significant abatement of subsurface warming after 2015 and consider when – or if – the Gulf of California will return to a ‘normal’ state like that prior to 2010. Despite the potential for shifting to a cooler oceanic regime, the small phenotype for jumbo squid has persisted until present (2022), and the overall trajectory of ecological recovery is unclear. Integrated analyses of additional oceanographic and biological time-series, fisheries records, and other data will be necessary to identify critical processes and trajectories occurring in the Gulf of California.

Early Life History and Recruitment Processes of a Tropical Anguillid Eel Anguilla marmorata to the Pacific Coast, as Revealed by Otolith Sr:Ca Ratios and Microstructure.

Recent progress in otolith microchemistry especially in strontium:calcium (Sr:Ca) ratios has revealed significant features of life histories in fishes. A catadromous eel, Anguilla marmorata, has the widest distribution among anguillid eels throughout the Indo-Pacific region. However, its dispersal and recruitment mechanisms in the ocean are still unknown. The temporal and spatial variations of early life history characteristics in a tropical anguillid eel A. marmorata were examined by means of otolith Sr:Ca ratios and microstructure to understand the larval transport and recruitment processes to the coasts in the Pacific region. Durations of the larval stage and age at recruitment to the southern part of Japan ranged from 79 to 157 d and 113 to 192, respectively. No significant differences were found between recruitment months in those parameters. The early life characteristics such as larval duration and age at recruitment were constant throughout the recruitment period in the southern part of Japan. The early life history characteristics in combination with the oceanic current regime possibly determine the larval transportation and dispersion processes and further recruitment dynamics to the Pacific coast of A. marmorata. The present study also provides useful information on its biogeographic distribution in the species as determined by otolith Sr:Ca ratios and microstructure.