Impact of a warm anomaly in the Pacific Arctic region derived from time-series export fluxes

Unusually warm conditions recently observed in the Pacific Arctic region included a dramatic loss of sea ice cover and an enhanced inflow of warmer Pacific-derived waters. Moored sediment traps deployed at three biological hotspots of the Distributed Biological Observatory (DBO) during this anomalously warm period collected sinking particles nearly continuously from June 2017 to July 2019 in the northern Bering Sea (DBO2) and in the southern Chukchi Sea (DBO3), and from August 2018 to July 2019 in the northern Chukchi Sea (DBO4). Fluxes of living algal cells, chlorophyll a (chl a), total particulate matter (TPM), particulate organic carbon (POC), and zooplankton fecal pellets, along with zooplankton and meroplankton collected in the traps, were used to evaluate spatial and temporal variations in the development and composition of the phytoplankton and zooplankton communities in relation to sea ice cover and water temperature. The unprecedented sea ice loss of 2018 in the northern Bering Sea led to the export of a large bloom dominated by the exclusively pelagic diatoms Chaetoceros spp. at DBO2. Despite this intense bloom, early sea ice breakup resulted in shorter periods of enhanced chl a and diatom fluxes at all DBO sites, suggesting a weaker biological pump under reduced ice cover in the Pacific Arctic region, while the coincident increase or decrease in TPM and POC fluxes likely reflected variations in resuspension events. Meanwhile, the highest transport of warm Pacific waters during 2017–2018 led to a dominance of the small copepods Pseudocalanus at all sites. Whereas the export of ice-associated diatoms during 2019 suggested a return to more typical conditions in the northern Bering Sea, the impact on copepods persisted under the continuously enhanced transport of warm Pacific waters. Regardless, the biological pump remained strong on the shallow Pacific Arctic shelves.

Diffusion controls the ventilation of a Pacific Shadow Zone above abyssal overturning

Mid-depth North Pacific waters are rich in nutrients and respired carbon accumulated over centuries. The rates and pathways with which these waters exchange with the surface ocean are uncertain, with divergent paradigms of the Pacific overturning: one envisions bottom waters upwelling to 1.5 km depth; the other confines overturning beneath a mid-depth Pacific shadow zone (PSZ) shielded from mean advection. Here global inverse modelling reveals a PSZ where mean ages exceed 1400 years with overturning beneath. The PSZ is supplied primarily by Antarctic and North-Atlantic ventilated waters diffusing from below and from the south. Half of PSZ waters re-surface in the Southern Ocean, a quarter in the subarctic Pacific. The abyssal North Pacific, despite strong overturning, has mean re-surfacing times also exceeding 1400 years because of diffusion into the overlying PSZ. These results imply that diffusive transports – distinct from overturning transports – are a leading control on Pacific nutrient and carbon storage.

Distribution of eggs and adults of alaska plaice Pleuronectes quadrituberculatus and flathead sole Hippoglossoides elassodon (Pleuronectidae) in the Pacific waters of Kamchatka

Distribution and biological parameters are considered for eggs and adults of two flatfish species on the data of annual surveys conducted on the shelf of southeastern Kamchatka in summer of 2011–2014 and 2016–2019. The eggs of Pleuronectes quadrituberculatus were sampled mostly at the stage of a germinal strip forming, whereas the eggs of Hippoglossoides elassodon were mostly at the stage of embryo cleavage. The main congestions of the eggs were found in the Kronotsky Bay and northern Avachinsky Bay. The adults of both species concentrated mainly in the northern Kronotsky Bay, at Cape Povorotny. Old age groups prevailed in aggregations of P. quadrituberculatus, but middle-age and young fish — in the aggregations of H. elassodon.

Information support for chub mackerel Scomber japonicus fishery in the Pacific waters of the Russian Federation

Methods of machine learning were applied for forecasting of chub mackerel fishing grounds in the South Kuril fishery district. The problem of perspective fishing area definition was reduced for a binary classification task, i.e. the sets of environmental conditions corresponded with presence or absence of fishing operations were determined for each point within the district. The fishery statistics for 2016–2020 and the data on SST with delay of 4–7 days from the date of catch, spatial SST gradients calculated using Belkin algorithm, and day-to-day SST variations were processed using LightGBM machine learning algorithm. The model was trained on the data for 2016–2019 and verified on the data for 2020. The AUC (as an aggregate measure of performance across all possible classification thresholds) varied from 0.65 to 0.92. In the fishery season of 2020, AUC was 0.69, on average, growing to 0.75 in the period of the highest catches. Approximately 75 % of the annual catch of chub mackerel was caught at the predicted sites in 2020; this portion reached 84 % in the period of the highest catches.

First record of genus Phlyctaenopora in South Pacific waters

Four species of Phlyctaenopora Topsent, 1904 (Demospongiae Sollas, Poecilosclerida Topsent, Mycalidae Lundbeck) are recognised today (Van Soest et al. 2021a) (Table 1): two Atlantic Ocean species in subgenus Phlyctaenopora [type species P. (P.) bitorquis Topsent, 1904, from the Azores; P. (P.) halichondrioides van Soest & Stentoft, 1988, from Barbados]; and two Southern Hemisphere species in subgenus Barbozia Dendy, 1922: P. (Barbozia) primitiva Dendy, 1922, from the Seychelles, and P. (B.) bocagei Lévi & Lévi, 1983, from New Caledonia. Here we describe a new species of Phlyctaenopora from Wanganella North in International Waters on the West Norfolk Ridge, northwest of New Zealand. Phlyctaenopora (B.) spina sp. nov. provides a first record of the genus in the South Pacific, providing further confirmation of the integrity of the subgenus Barbozia.

Spatial Distribution and Abundance of Small Cetaceans in the Pacific Waters of Guatemala

The establishment of marine protected areas (MPAs) requires a thorough assessment of the abundance, distribution, and habitat preferences of a variety of marine species. Small cetacean spatial distribution and abundance were examined in the Pacific waters of Guatemala to provide this information. Boat surveys were conducted for 38 months between January 2008 and June 2012. A total of 64,678 cetaceans in 505 sightings from nine Delphinidae species were recorded. Three species, referred to as common species, accounted for 90% (n = 456) of all sightings. They included Tursiops truncatus (56%, n = 278), Stenella attenuata (29%, n = 143), and Stenella longirostris (7%, n = 35). Group size was significantly different among the common species (p < 0.001). S. longirostris had the largest group size (444 ± 75 dolphins), followed by S. attenuata (28 ± 5 dolphins), and T. truncatus (15 ± 2 dolphins). T. truncatus was the most common in the study area (0.02 ± 0.002 sightings/km of survey effort), and S. attenuata (0.37 ± 0.16 dolphins/km) and S. longirostris (1.62 ± 0.41 dolphins/km) were the most abundant in the neritic (≤200 m depth) and oceanic zones (≥200 m depth), respectively. The wide-ranging distribution of T. truncatus overlapped with the distribution of S. attenuata in the neritic zone and S. longirostris in the oceanic zone. Little overlap was observed in the distribution of S. attenuata and S. longirostris. Most hot spots (∼66%) were in the oceanic zone and no hot spots were near or in the MPAs. Hot spots were identified along the 200 m isobath, the Middle America trench, and the San José Canyon. These could be areas of high productivity where dolphins concentrate to feed. To the north of the San José Canyon, five species of small cetaceans were observed in a stretch of the neritic zone including three MPAs. No other section of this zone had such high diversity. Results need to be taken with caution given the small sample size. Our results suggest that the protection of small cetaceans needs to consider the creation of oceanic MPAs that should be integrated into the existing network.

«Wrong fish» or wrong hypotheses: what happens to nekton of the Pacific waters at Kuril Islands?

A phenomenon of undulating fluctuations of nekton abundance in the Kuroshio system is discussed on example of japanese sardine Sardinops melanostictus, as the most abundant and the most fluctuating species. The so-called «sardine epochs» are distinguished according to this species abundance. The last such epoch ended in the early 1990s. Since 2014, structural changes occurred again in the nekton communities of the Pacific waters off Kuril Islands, caused by expansion of southern fish and squid species, primarily japanese sardine and chub mackerel Scomber japonicus, and decreasing in abundance of japanese anchovy Engraulis japonicus and saury Cololabis saira. The scope of these changes allowed Russian fishermen to resume the fishery on japanese sardine and chub mackerel in the Russian exclusive economic zone since 2016. Annual catch of Japanese sardine increased steadily from 6,700 t in 2016 to 315,500 t in 2020. Over these 5 years, Russian fishermen landed 531,700 t of sardine and 167,900 t of chub mackerel. However, many Russian fishery forecasters believe that these reconstructions is only a «rehearsal» of the upcoming «sardine epoch», being based on formal climatic indices, without delving into the mechanisms of abundance fluctuations. The authors note that new «sardine epochs» cannot be predicted as completely similar to the previous ones. Several hypotheses on causes of the beginning and end of japanese sardine blooms are considered critically, and the conclusion is made that mechanisms which determine its year-classes strength are still unclear, as well as the reasons of undulating fluctuations of this species and some other nekton species abundance, because of high complexity of this problem.

Numerical modeling of the consequences of "marine heatwaves" in the North Pacific for the Arctic Ocean

<p>As a result of the analysis of the NOAA surface temperature observational data (Huang et al., 2020), the periods corresponding to "marine heatwaves" in the northeastern Pacific Ocean (2013-2019) were identified. Marine heatwaves were defined as exceeding the 90th percentile threshold. The same analysis of the temperature in the Bering Strait's immediate vicinity showed anomalously warm waters in the same years. Analysis of the pressure field, which forms the atmosphere's dynamic state and affects the water circulation system of the Bering Sea, allowed us to assume the inflow of anomalously warm Pacific waters into the Chukchi Sea. To analyze the North Pacific heatwaves' consequences for the Arctic Ocean, we carried out two numerical experiments using the regional ocean and sea ice model SibCIOM (Golubeva et al., 2018) and NCEP/NCAR atmospheric reanalysis data (Kalnay et al., 1996). The first numerical experiment was carried out to calculate hydrodynamic and ice fields from January 2000 to November 2020 (Experiment 1). On the Arctic and the Pacific Ocean boundary in the Bering Strait, we used the monthly average climatic values ​​of the transport, temperature, and salinity of waters coming from the Pacific Ocean. Experiment 2 was carried out from 2014 to November 2020. The calculated values ​​of hydrological and ice characteristics obtained in Experiment 1 were used as the initial state for this experiment. In contrast to Experiment 1,  a heat flux exceeding the average climatic values ​​was set at the Bering Strait in Experiment 2. Its assignment was provided by using temperature values ​​from observational data in the Bering Strait vicinity (Huang et al., 2020). Comparison of monthly average hydrological and ice fields obtained in two numerical experiments and analysis of numerical results showed that an increase in the temperature of the Pacific waters entering the Arctic shelf through the Bering Strait leads to an increase in the heat content of the Chukchi Sea waters, heat transfer by currents in the surface and subsurface layers, a gradual increase in the heat content of the Beaufort Sea, and the reduction of Arctic ice cover. The increase in heat content in Experiment 2 for the Beaufort Sea was obtained in both the upper 50-meter and 250-meter layers.</p><p>The research is supported by the Russian Science Foundation, grant №. 19-17-00154.</p>