Factors Influencing the Interannual Variation in Biomass of Bottom-Cultured Yesso Scallop (Patinopecten yessoensis) in the Changhai Sea Area, China

Understanding how environmental factors impact the interannual variation in scallop growth and subsequently developing an easily obtained parameter to indicate this variation could provide a scientific basis for optimizing their aquaculture. In this study, we have set a growth scenario of uniformly sowed scallops of the same initial size in the Changhai sea area. The Yesso scallop culture ecosystem model was used to simulate the growth of bottom-cultured Yesso scallop each year from December 1, 2006 to November 30, 2017. The results show that the annual growth rate was higher in the northwest than in the southeast, and there were obvious high-value areas near the islands. The scallop biomass was significantly lower in 2009–2010 and reached its highest point in 2013–2014. Based on the match-mismatch conditions of bottom-water temperature, food availability, and the Yesso scallop growth process, three factors were determined: suitable growth days (SGD), restricted growth days (RGD), and food accumulation (FA). Subsequently, a multiple regression relationship was proposed with scallop biomass to explore the reasons affecting the interannual variations in scallop growth. We found that the anomaly of the contribution of SGD and FA for the scallop growth was small, and the interannual variation in scallop biomass was mainly regulated by RGD in winter. Our results indicated that the interannual variation in RGD in winter was closely related to the regional averaged air temperature in early winter. The air temperature in early winter is easily obtained in practice. Consequently, it could be used to predict the interannual growth of bottom-cultured scallops to improve aquaculture planning and management.

Landscape Mapping, Ichnological and Benthic Foraminifera Trends in a Deep-Water Gateway, Discovery Gap, NE Atlantic

Multidisciplinary studies have allowed us to describe the abiotic landscapes and, thus, reveal the ichnological and benthic foraminifera trends in a deep-water gateway. Mesoscale landscape mapping is presented based on the bathymetric position index, substrate types and near-bottom water temperature. Four sediment cores, retrieved from the entrance, centre and exit of the gap, were subject to computed tomography, ichnological and benthic foraminifera studies. A high diversity of abiotic landscapes in the relatively small area of Discovery Gap is detected and its landscape is characterized by 23 landscape types. The most heterogeneous abiotic factor is a topography that is associated with sediment patchiness and substrate variability. The ichnological and tomographical studies of the sediment cores demonstrate lateral and temporal differences in the macrobenthic tracemaker behaviour. The ichnofossils assemblage of the sediment core can be assigned to the Zoophycos ichnofacies with a higher presence of Zoophycos in the entrance site of the gap and during glacial intervals. Higher benthic foraminifera diversity and species richness during the Holocene are also registered in the southern part of the gap compared to the northern part. The spatial and temporal differences in macro-benthos behavior and benthic foraminifera distribution in the deep-water gateway are proposed to relate to the topographical variations of the Antarctic Bottom Water and its influence on the hydrodynamic regime, nutrient transport, etc.

The Early Paleogene Succession at Tora, New Zealand; Stratigraphy and Paeloclimate: A Critical North Island Eocene Temperature Record and a Crucial Linkage Between the Depositional Settings of the Central and Southern East Coast Basin

<p>This study has utilised the Mg/Ca paleothermometry method to provide a new, North Island reference of sea temperatures in the Southwest Pacific during a period of extreme global warming, referred to as the Early Eocene Climatic Optimum (EECO; ~53-50 Ma). This period of Earth’s history is of great interest as it represents the warmest climates of the Cenozoic. Importantly the climate dynamics of this period as simulated by computer models do not appear to match paleo-proxy data, specifically with regard to the latitudinal distribution of heat. Development of this paleoceanographic record involved detailed mapping of three sections in the Wairarapa region (41.506199 S, 175.517663 E) of New Zealand’s North Island. Three primary stratigraphic sections (Pukemuri, Awheaiti and Te Oroi Streams) were described and dated using foraminiferal and calcareous nannofossil biostratigraphy, with supplementary observations and measurements included from sections at Manurewa and Te Kaukau Points. These sediments are primarily siliciclastic sandstones and mudstones in composition, and sedimentary structures within these sections include turbidite sequences, channelisation and synsedimentary slumping, suggesting the EECO interval here is represented by sedimentation within a mid-bathyal submarine channel and fan environment. In contrast, the Early Paleocene Manurewa and Awhea Formations have previously been interpreted as a shallow, marginal marine environment which is at odds with benthic foraminiferal paleodepth indicators and trace fossil assemblages identified in this study. Selected genera of planktic foraminifera were extracted from the EECO interval and paleo-water temperatures determined from Mg/Ca values measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICPMS). This method was selected as it allows specific targeting of analysis sites, enabling avoidance of contaminated and altered parts of the test. This method also provides simultaneous measurements of other trace elements (Al, Si, Ti, Mn, Zn, Sr, Ba) that can be used as a guide to preservation state of the test (for example, Al, Ti and Si are considered indicators of detrital contamination levels). Four foraminifera genera were selected as suitable paleotemperature indicators of separate components of the water column. Morozovella spp. and Acarinina spp. were selected for surface mixed layer paleotemperature estimates, Subbotina spp. for thermocline temperature values, and Cibicides spp. for bottom water temperature determinations.SEM images, combined with trace element data were used to parse the resulting Mg/Ca data and only those that met strict quality criterion, including low detrital contamination and lack of visual evidence for recrystalisation were used for temperature reconstruction. Planktic Mg/Ca data were converted to temperature using the relationship (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.38 0.09 × T) and benthic Mg/Ca temperatures calculated using (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.87 0.109 × T), each assuming an early Eocene seawater Mg/Ca value of 4.1 mol/mol. Calibrated Mg/Ca results show peak sea surface temperatures of 29°C for Morozovella and Acarinina in the East Coast Basin during the Early Eocene, with bottom water temperatures of 17°C obtained from Cibicides. These data are consistent with the high sea surface temperatures reconstructed by previous workers in the nearby Canterbury Basin. The data from this new reference point support the idea that the EECO was characterised by a lower, possibly absent latitudinal temperature gradient in the midlatitude Southwest Pacific, than numerical models suggest, indicating a fundamental gap in the knowledge of climate dynamics in conditions much warmer than today.</p>

The Early Paleogene Succession at Tora, New Zealand; Stratigraphy and Paeloclimate: A Critical North Island Eocene Temperature Record and a Crucial Linkage Between the Depositional Settings of the Central and Southern East Coast Basin

<p>This study has utilised the Mg/Ca paleothermometry method to provide a new, North Island reference of sea temperatures in the Southwest Pacific during a period of extreme global warming, referred to as the Early Eocene Climatic Optimum (EECO; ~53-50 Ma). This period of Earth’s history is of great interest as it represents the warmest climates of the Cenozoic. Importantly the climate dynamics of this period as simulated by computer models do not appear to match paleo-proxy data, specifically with regard to the latitudinal distribution of heat. Development of this paleoceanographic record involved detailed mapping of three sections in the Wairarapa region (41.506199 S, 175.517663 E) of New Zealand’s North Island. Three primary stratigraphic sections (Pukemuri, Awheaiti and Te Oroi Streams) were described and dated using foraminiferal and calcareous nannofossil biostratigraphy, with supplementary observations and measurements included from sections at Manurewa and Te Kaukau Points. These sediments are primarily siliciclastic sandstones and mudstones in composition, and sedimentary structures within these sections include turbidite sequences, channelisation and synsedimentary slumping, suggesting the EECO interval here is represented by sedimentation within a mid-bathyal submarine channel and fan environment. In contrast, the Early Paleocene Manurewa and Awhea Formations have previously been interpreted as a shallow, marginal marine environment which is at odds with benthic foraminiferal paleodepth indicators and trace fossil assemblages identified in this study. Selected genera of planktic foraminifera were extracted from the EECO interval and paleo-water temperatures determined from Mg/Ca values measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICPMS). This method was selected as it allows specific targeting of analysis sites, enabling avoidance of contaminated and altered parts of the test. This method also provides simultaneous measurements of other trace elements (Al, Si, Ti, Mn, Zn, Sr, Ba) that can be used as a guide to preservation state of the test (for example, Al, Ti and Si are considered indicators of detrital contamination levels). Four foraminifera genera were selected as suitable paleotemperature indicators of separate components of the water column. Morozovella spp. and Acarinina spp. were selected for surface mixed layer paleotemperature estimates, Subbotina spp. for thermocline temperature values, and Cibicides spp. for bottom water temperature determinations.SEM images, combined with trace element data were used to parse the resulting Mg/Ca data and only those that met strict quality criterion, including low detrital contamination and lack of visual evidence for recrystalisation were used for temperature reconstruction. Planktic Mg/Ca data were converted to temperature using the relationship (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.38 0.09 × T) and benthic Mg/Ca temperatures calculated using (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.87 0.109 × T), each assuming an early Eocene seawater Mg/Ca value of 4.1 mol/mol. Calibrated Mg/Ca results show peak sea surface temperatures of 29°C for Morozovella and Acarinina in the East Coast Basin during the Early Eocene, with bottom water temperatures of 17°C obtained from Cibicides. These data are consistent with the high sea surface temperatures reconstructed by previous workers in the nearby Canterbury Basin. The data from this new reference point support the idea that the EECO was characterised by a lower, possibly absent latitudinal temperature gradient in the midlatitude Southwest Pacific, than numerical models suggest, indicating a fundamental gap in the knowledge of climate dynamics in conditions much warmer than today.</p>

Geothermal heating and episodic cold-seawater intrusions into an isolated ridge-flank basin near the Mid-Atlantic Ridge

Six-year records of ocean bottom water temperatures at two locations in an isolated, sedimented deep-water (∼4500 m) basin on the western flank of the mid-Atlantic Ridge reveal long periods (months to >1 year) of slow temperature rises punctuated by more rapid (∼1 month) cooling events. The temperature rises are consistent with a combination of gradual heating by the geothermal flux through the basin and by diapycnal mixing, while the sharper cooling events indicate displacement of heated bottom waters by incursions of cold, dense bottom water over the deepest part of the sill bounding the basin. Profiles of bottom water temperature, salinity, and oxygen content collected just before and after a cooling event show a distinct change in the water mass suggestive of an incursion of diluted Antarctic Bottom Water from the west. Our results reveal details of a mechanism for the transfer of geothermal heat and bottom water renewal that may be common on mid-ocean ridge flanks.

Southern Ocean bottom-water cooling and ice sheet expansion during the middle Miocene climate transition

The middle Miocene climate transition (MMCT), around 14 Ma, was associated with a significant climatic shift, but the mechanisms triggering the event remain enigmatic. We present a clumped isotope (Δ47) bottom-water temperature (BWT) record from 16.0 to 12.2 Ma from Ocean Drilling Program (ODP) Site 747 in the Southern Ocean and compare it to existing BWT records from different latitudes. We show that BWTs in the Southern Ocean reached 8–10 ∘C during the Miocene climatic optimum. These high BWT values indicate considerably warmer bottom-water conditions than today. Nonetheless, bottom-water δ18O (calculated from foraminiferal δ18O and Δ47) suggests substantial amounts of land ice throughout the interval of the study. Our dataset further demonstrates that BWTs at Site 747 were variable with an overall cooling trend across the MMCT. Notably, a cooling of around 3–5 ∘C preceded the stepped main increase in benthic δ18O, interpreted as global ice volume expansion, and appears to have been followed by a transient bottom-water warming starting during or slightly after the main ice volume increase. We speculate that a regional freshening of the upper water column at this time may have increased stratification and reduced bottom-water heat loss to the atmosphere, counteracting global cooling in the bottom waters of the Southern Ocean and possibly even at larger scales. Feedbacks required for substantial ice growth and/or tectonic processes may have contributed to the observed decoupling of global ice volume and Southern Ocean BWT.

Deglacial bottom water warming intensified Arctic methane seepage in the NW Barents Sea

Changes in the Arctic climate-ocean system can rapidly impact carbon cycling and cryosphere. Methane release from the seafloor has been widespread in the Barents Sea since the last deglaciation, being closely linked to changes in pressure and bottom water temperature. Here, we present a post-glacial bottom water temperature record (18,000–0 years before present) based on Mg/Ca in benthic foraminifera from an area where methane seepage occurs and proximal to a former Arctic ice-sheet grounding zone. Coupled ice sheet-hydrate stability modeling shows that phases of extreme bottom water temperature up to 6 °C and associated with inflow of Atlantic Water repeatedly destabilized subsurface hydrates facilitating the release of greenhouse gasses from the seabed. Furthermore, these warming events played an important role in triggering multiple collapses of the marine-based Svalbard-Barents Sea Ice Sheet. Future warming of the Atlantic Water could lead to widespread disappearance of gas hydrates and melting of the remaining marine-terminating glaciers.

Lunar Periodicity in Reproduction of Senatorial Scallop (Chlamys Senatoria Gmelin, 1791) in Asid Gulf, Masbate, Philippines

In Masbate, senatorial scallop Chlamys senatoria is one of the five commercially important species of scallop present in Asid Gulf, but its basic biology is poorly understood in the Philippines. To provide biological information for future conservation and management, the reproductive rhythm of senatorial scallop in relation to lunar phase was investigated from October 2016 to March 2017. Scallops were collected daily from the fishers’ catches and were measured, dissected, and processed for histological analysis; whereas, fecundity and size of eggs (diameter) were also determined. Ecological parameter such as bottom water temperature was monitored during the sampling period. Results showed that C. senatoria is a highly fecund species, which ranges from 8.3 X 105 to 2.1 X 106 oocytes per female and its sizes (oocytes) ranges from 53.8 µm to 72.5 µm while Gonado-somatic index (GSI) ranges from 3.2 to 7.1. Fecundity, egg diameter, and the GSI decreased during new moon (NM) and full moon (FM). GSI indicates that the onset of spawning activity commences during NM and FM. Environmental parameters that were monitored showed significant variations in relation to lunar phase. Spawning of scallop C. senatoria follows a lunar reproductive pattern, which was initiated and influenced by the variations of different factors such as temperature, water amplitude, and light as the effect of lunar/tidal cycles. These findings indicate that reproduction and necessarily spawning in the scallop are related to factors associated with lunar phases. Strategies for managing the resource can be formulated using the temporal dimension of lunar phases.

Oxygen Isotope Offsets in Deep-Water Benthic Foraminifera

ABSTRACT Despite the extensive use of the benthic foraminiferal oxygen isotope composition (δ18O) as a proxy for paleoclimatic reconstructions, uncertainties remain regarding the consistency of interspecies offsets and the environmental factors controlling 18O fractionation. We investigated δ18O offsets of some frequently used Uvigerina, Bulimina, and Cibicidoides species in core top samples from different hydrographic and sedimentary regimes in the South China Sea, Makassar Strait, and Timor Strait/Eastern Indian Ocean. The δ18O values of the epifaunal taxa Cibicidoides mundulus and Cibicidoides wuellerstorfi showed no significant offset in all investigated regions, whereas shallow infaunal Cibicidoides species exhibited higher variability and were less reliable. We found no offsets between species of Uvigerina and Bulimina and assume that these genera can be measured together and/or substituted. Our results show that epifaunal taxa are close to equilibrium with ambient seawater and thus provide more reliable records of past ice volume and/or bottom water temperature variations than infaunal taxa. Offsets among equilibrium calcite, epifaunal taxa, and infaunal taxa are not constant “vital effects” but are influenced by changing gradients in bottom to pore water pH and carbonate ion concentrations that depend on deep-water ventilation and export flux of particulate carbonate and organic carbon. Offsets between epifaunal and infaunal taxa varied between 0.58 and 0.73‰, depending on regional bottom and pore water conditions. Our findings highlight the importance of regional and temporal variations in organic carbon flux/degradation and dissolution of calcite that may lead to slight under- or overestimates of the amplitude of δ18O fluctuations, especially during times of rapidly changing calcite-saturation of bottom and pore water.

Seasonal variability of natural methane seepage offshore Western Svalbard

&lt;p&gt;Natural methane seepage from the seafloor to the water column occurs worldwide in marine environments, from continental shelves to deep-sea basins. Depending on water depth, methane fluxes, and mixing rate of the seawater, methane may partially reach the atmosphere, where it could contribute to the global greenhouse effect. Estimates of annual marine methane fluxes are commonly calculated from hydro-acoustic data collected during single research surveys. These snapshot estimates neglect short (i.e., tide) and long (seasonal) variations.&lt;/p&gt;&lt;p&gt;Here we compare the seepage activity along the upper limit of the gas hydrate stability zone offshore Western Svalbard in August 2017 (bottom water temperature (BT) ~3.46&amp;#176;C), June 2020 (BT ~1.75&amp;#176;C), and November 2020 (BT ~3.96&amp;#176;C) using high-resolution vessel-based multibeam data. Our results complete annual methane flux estimates by Ferr&amp;#233; et al. (2020) and confirm a significantly reduced seepage activity during the cold bottom-water conditions. We investigate short-term variation by comparing a 7.5 km long multibeam section at three phases of the lunar semidiurnal (M2) tide. We will discuss how these processes affect annual methane fluxes estimates offshore Svalbard and further Arctic methane fluxes estimates.&lt;/p&gt;&lt;p&gt;The research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) and is supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259 and UiT.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Ferr&amp;#233;, B., Jansson, P. G., Moser, M., Serov, P., Portnov, A., Graves, C. A., et al. (2020). Reduced methane seepage from Arctic sediments during cold bottom-water conditions. Nat. Geosci. 13, 144&amp;#8211;148. DOI: 10.1038/s41561-019-0515-3&lt;/p&gt;