Deep-sea Research Part Ii-topical Studies in Oceanography最新文献

We describe the first year-long hydrographic mooring timeseries from a location just to the south of the Drygalski Ice Tongue – the ice margin that forms the southern boundary of the Terra Nova Bay Polynya in the western Ross Sea. The region is where any northward flowing component of the Victoria Land Coastal Current encounters the ice tongue and supports an occasional polynya. The hydrographic mooring was deployed nearby Geikie Inlet from February 2017 through to March 2018, and was coupled with several contemporaneous oceanographic moorings to the north of the Drygalski Ice Tongue. This provides data with which to examine the water column dynamics in the context of local circulation and interaction with the ice tongue. The Terra Nova Bay region is subject to strong katabatic winds, however the polynya to the south of the Drygalski Ice Tongue operates at different times through the annual cycle when compared to the Terra Nova Bay Polynya to the north, as the sea ice in the south-side region is far more constrained in its motion yet, temperature and salinity are broadly consistent north and south of the ice tongue. Sub-surface Ice Shelf Water is observed south of the ice tongue. Transients in near-bed temperature and salinity are observed on both sides of the ice tongue, albeit with the northside leading by ∼8–9 days. Notably, the temperature transient precedes that of salinity by around 40 days. This suggests that, at this near-coastal position, the circulation beneath the ice tongue is primarily southward.

Literature on Ross Sea zooplankton is limited, although it is the most productive system and has the highest biomass of phytoplankton in the Southern Ocean. Energy transfer within the food web and response of continental shelf food web to climate change depend on the knowledge of the density and distribution of zooplankton. We evaluated its density, composition, spatial distribution and their potential relations with environmental factors and specific water mass presence. Particular attention was given to copepods. Mesozooplankton samples were collected between 14 January and February 11, 2017 from 14 stations in the western Ross Sea and Terra Nova Bay, while other micronekton samplings were completed at 6 stations. Results highlighted three pools of stations: one inside Terra Nova Bay with the highest densities, one on the platform with lower mean density, and the third represented by a N–S transept at 175°E with the lowest mean density. This partitioning of the region fit with the grouping of stations according to a ternary plot based on the different percentages of water masses in each station and reflected the similarity of zooplankton. The presence of specific water masses and their contribution in the upper 200 m influences zooplankton biodiversity and density. A phylogenetic tree of the zooplankton was constructed to analyse the distance among the observed taxa. The area located near the coast exhibited the highest degree of phylogenetic overdispersion. In coastal waters, typical copepod species constituted the main part of the neritic zooplankton of Terra Nova Bay and Ross Sea. Oithona similis was the most abundant species both in coastal and offshore sectors, followed by pteropods, polychaetes and euphausiids.

The Greenland Ice Sheet releases fresh water from ice melt, tundra snow melt, and solid ice at an increasing rate during recent decades resulting in an increasing amount of freshwater runoff into the ocean. As a result, freshwater runoff is changing the continental shelf circulation by increasing the amount of fresher water on the shelf that may then enter the deep ocean. Observational studies show that dense water does traverse the east Greenland shelf near the ocean bottom but it is unclear to what extent the transport of near surface fresh water, as a result of runoff, reaches deeper water and enters the Irminger Basin. Using 4 km resolution nested numerical model simulations with and without freshwater runoff, we show freshwater runoff increases salinity variability with increased baroclinicity. While higher salinity variability and baroclinicity suggest a greater potential for water mass exchange across the East Greenland Current, most freshwater runoff along east Greenland remains on the shelf. From freshwater runoff alone, salinity and salt mass decreases by 0.22% on the continental shelf compared to a 0.01% in the rest of the Nordic Seas. There is a 0.05% reduction in salt mass on the Greenland shelf region that makes up 8% of the simulation domain, suggesting little water exits the shelf along the east coast of Greenland. The largest reduction in salt mass occurs around Iceland, where substantial freshwater runoff exists. A calculation of baroclinic conversion rate suggests likely pathways for runoff to exit the continental shelf and enter deep water in the Denmark Strait and over the Greenland/Scottland ridge east of Iceland. Most of the fresh water, however, released along the east coast of Greenland continues towards Cape Farewell, outside our modeling domain, and into the Labrador Sea.

This paper explores the habitat characteristics of commercial tuna species based on daily oceanography parameters in the Eastern Indian Ocean Off Java-Bali Waters. Moreover, more research is needed combining the daily spatial distribution of oceanographic variables of surface and sub-surface data to analyse the habitat characteristics of large pelagic fish, including tuna species. In this study, we used five main daily oceanography parameters: sea surface temperature (SST), sea surface chlorophyll (CHLa), sea surface height (SSH), dissolved oxygen at 100m (DO100), the temperature at 100m (temp100) and the combination of the catch of yellowfin (YFT), albacore (ALT) and bigeye (BET) tuna that use long lines. To analyse the relationship between the environmental database and tuna catch, we utilized Generalized Additive Models (GAMs) from univariate variables until the combination of all variables. The result stated that all the variables influence the existence of all tuna species with P-values <0.001. Temperature is the most critical predictor variable, SST is the most vital predictor for BET and YFT tuna, and temp100 is the most critical for ALT. The second most essential variables were DO100 for BET, Temp 100 for YFT, and SSH for ALT. Moreover, BET and YFT prefer to stay at a lower temp100, and ALT tuna remains at a higher temp100. However, all of them avoid an SST higher than 29 °C. Further assessment of the long-term SST trend specific to tuna species is required to fully account for the effects of global warming on the oceans.

An international conference on the oceanography of the Ross Sea was held in Naples, Italy in July 2023. A total of 75 abstracts were presented orally, and 20 presented as posters. Researchers from 11 countries attended, with conference support from a variety of public and private firms. The conference was held under the patronage of the United Nations Decade of Ocean Science for Sustainable Development, the Southern Ocean Observing System, the Ministero dell’Università e della Ricera, the Programma Nazionale di Recerche in Antartide, and the Commissione Oceanografica Italiana, and was organized by Parthenope University of Naples and Marche Polytechnic University of Ancona. The papers included were either presented at the meeting or were closely related to the conference's goals and program. The conference maintained Italy's long tradition of hosting engaging conferences on oceanographic research in the Ross Sea.

Numerous temporal and spatial patterns of natural climate variability have been characterized. By analyzing standardized and detrended sea surface temperature anomalies (SSTA) along the coast from 1950 to 2023, this study identifies two dominant modes of ocean variability in the Northeast Pacific Boundary Current (NEPBC) which includes the California and Alaska currents. The first mode is the prevalent pattern of interannual variability associated with the El Niño-Southern Oscillation. A second mode arises as an independent dipole between the coasts of North and Central America, with the strongest intensities on a portion of the NEPBC (38°-53°N) and the Eastern Pacific warm pool (EPWP, 2°S-15°N). The difference in SSTA between the two regions appears to be caused by variations in the intensity and distribution of atmospheric pressure fields and it is related with the Pacific Meridional Mode and North Pacific Oscillation. Such coastal mode will provide the opportunity to describe the interactions of coastal processes with climate indices capturing larger-scale phenomena.

The formation of Arabian Sea High Salinity Water (ASHSW) during the winter monsoon in the northern Arabian Sea is driven by surface buoyancy loss, which increases surface density and triggers convective mixing. The depth of convective mixing is influenced by the interplay between surface cooling (buoyancy loss) and upper-ocean stratification. Mesoscale eddies present during winter can alter this stratification and modulate convective mixing. We investigated the impact of these eddies on convective mixing and ASHSW formation utilizing a combination of observations, data assimilative model results, and 1-D and 3-D model experiments. Our analyses consistently demonstrate that the depth of winter convective mixing is influenced by the stratification imposed by mesoscale features, resulting in distinct mixing characteristics. When subjected to identical buoyancy forcing, convective mixing associated with cyclonic eddies occurs at shallower depths compared to anticyclonic eddies. This difference is particularly pronounced during the peak period of convective mixing (January–February), exceeding 50 m, compared to the early stages (November–December). The combined effect of cyclonic and anticyclonic eddies generates spatially inhomogeneous convective mixing, which cannot be solely explained by buoyancy flux. These conclusions are supported by Argo observations and analyses of 1-D and 3-D model experiments. Overall, our study highlights the significant role of mesoscale eddies in modulating convective mixing and ASHSW formation in the northern Arabian Sea.

Moving weather systems determine the history of wind variations with patterns as the systems transit through the ocean. These weather systems are integrated entities that can provide a system level perspective. A vessel-based survey repeatedly occupying a 30-km transect 12 times in 36 h provided non-aliased measurements of velocity field that showed how the along-shelf transport varied by more than three-fold in response to a transiting high-pressure weather system following an atmospheric cold front. To further illustrate the impact of different weather systems, we analyzed time series data from moored ADCPs, which showed influence on the velocity field from infrequent summertime cold fronts and remote hurricanes moving through the region, one on the west and the other on the east of the study site. Rotary spectrum analysis showed that the flow field rotated mostly clockwise with a smaller but non-negligible counterclockwise component, consistent with near inertial oscillations mixed with weak tidal currents. A theoretical model is presented by a Laplace transform and a general relationship between the velocity field and forcing functions is obtained, which shows that the contributions to the rotary velocity field from various forcing functions are through mathematical convolutions between the forcing functions and the complex frictional-rotary inertial function (CFRIF). These convolutions include an integrated effect of history of the forcing. CFRIF is effectively a frictional rotary filter that favors inertial oscillations. The wind-stress induced velocity field over a few days is computed and it shows significant variations after the passage of a cold front, with a magnitude consistent with observations. The wind-stress induced velocity is a few times greater than the density driven flow during the ship-based observations. The weather systems passing through the region can impact coastal currents causing a great variability over short time scales.

Theories of ocean–atmosphere interaction during a Madden–Julian Oscillation (MJO) are generally based on a thermodynamic model with surface fluxes dictating changes in sea surface temperature. Evidence from a two month ocean glider deployment in early 2019 in the southeast Indian Ocean suggests the impact of mesoscale dynamics on upper-ocean stratification likely affects ocean–atmosphere interaction at MJO scales. Until mid-February, local surface fluxes consistent with a convectively suppressed MJO phase drove near-surface ocean evolution. With the advection of a fresh-core eddy to the glider location in late February, ocean dynamics then becomes an additional driver of this evolution by modulating local stratification and generating a barrier layer of ≈12 m thickness for 10 days. One-dimensional modelling experiments based on the ocean and atmospheric conditions experienced during our sampling period show that the ocean subsurface structure within the eddy induce changes in SST of physical significance for ocean-atmosphere interaction. Moreover, results also suggest that the presence of a thick eddy-induced barrier layer during the MJO suppressed phase modulates the magnitude of temperature anomalies forced by surface fluxes during the following enhanced MJO phase. As eddies are abundant in this area, their dynamics must be considered to correctly represent SST variability for MJO modelling.

The Antarctic environment offers a unique opportunity to study the interactions between Porifera and their microbial symbionts. Reports on the association between prokaryotes and Antarctic sponges are increasing. However, a comparison of the bacterial communities associated to the same sponge species but inhabiting different Antarctic areas has seldom been addressed. This study explored the prokaryotes associated with the sponge species Mycale (Oxymycale) acerata (Kirkpatrick, 1907) and Dendrilla antarctica (Topsent, 1905) collected from South Cove at Rothera Point (Antarctic Peninsula) and Thetys Bay (Ross Sea). In D. antarctica, some groups were equally represented at both sites (e.g., Amylibacter, Cutibacterium, Yoonia-Loktanella), whereas members in the genera Polaribacter and Kistimonas were more abundant in Rothera. Similarly, M. acerata individuals collected from Rothera showed a higher relative abundance of some bacterial genera, such as Polaribacter, Sulfitobacter, and Ulvibacter. The results allowed us to identify some taxa common to sponges belonging to the same species and highlighted the possible influence of site-specific environmental conditions in shaping symbionts.