Evidence of Deep DOC Enrichment via Particle Export Beneath Subarctic and Northern Subtropical Fronts in the North Pacific

Here we provide compelling evidence that deep particle export enhanced dissolved organic carbon (DOC) concentrations beneath the Pacific’s Subarctic Front (SA, ∼42°N) and Northern Subtropical Front (NST, ∼34°N). We report three main findings: First, deep export of subjectively small particles (128–512 μm) was apparent throughout the frontal zone in which the SA resides. However, export of large particles was specifically associated with the SA, rather than the entire frontal zone, and appeared to exclusively transfer DOC into the bathypelagic water column. Second, a similar DOC enrichment existed beneath the NST, though this signal was curiously not accompanied by observable particles (>128 μm). We conclude that export occurring previously in winter left this DOC behind as a residue, though the associated particles were no longer present by spring. Third, the presence of strong hydrographic fronts was not the only control on export that resulted in these unique DOC distributions. Deep export and DOC enrichment was also controlled by latitude-specific biogeochemical and hydrographic conditions, such as depth of the nutricline and seasonal mixed layer shoaling. Given these observations, the fronts within the transitional region of the North Pacific are clearly special locations for deep carbon sequestration and for providing uncommon DOC enrichment that ultimately supports the deep microbial community.

CHARACTERISTICS OF ANTICYCLONIC EDDY FORMED AT THE PACIFIC COAST OF THE SOUTHERN KURIL ISLANDS IN THE SPRING 1999

Based on the analysis of oceanographic survey materials and sea surface temperature satellite observations, the conditions of formation and characteristics of the anticyclonic eddy located in the region of the South Kuril Islands in the spring of 1999 were studied. It was shown that it separated from the subarctic front as result of its interaction with the Oyashio current stream in the second half of March and ceased to exist in mid-June, which is also confirmed by observations of the concentration of chlorophyll-a. In contrast the eddies formed as a result of meandering of the warm Kuroshio and Tsugaru currents, the eddy core, located at depths of 150–300 m, was characterized by lower values of temperature and salinity (4°–4.6°С and 33.55–33.65 е.п.с.) and low current velocities ( about 10 cm/s). The eddy was rather weakly distinguished in the density field both on horizontal and vertical distributions, as well as according to satellite altimetry data.

Abundance and ecology of Myctophidae fishes in the Gulf of Alaska in winter season

Distribution and abundance of myctophid fish species in the upper epipelagic layer are analyzed based on results of surveys in the Gulf of Alaska in winters of 2019 and 2020. A common myctophid community driven by blue lanternfish Tarletonbeania crenularis was revealed that occupied likely the entire eastern part of the Subarctic Front zone eastward from 150ºW. Abundance and biomass of four mass myctophid species were generally comparable between the northeastern and northwestern Pacific. Small-sized juveniles prevailed among northern lampfish Stenobrachius leucopsarus, which were likely transported by the Subarctic Current and could be recruited to the Bering Sea stock. Patterns of daily vertical migrations are discussed for the mass myctophid species. New observations confirm general understandings on the myctophid species input to functioning of fish community.

The influence of oceanological conditions on the location of pelagic fish fishing areas in the Pacific waters of the Kuril Islands during cold 2017 and warm 2018

Formation of the surface structure mechanism of the South Kuril waters in the last two years has undergone significant changes. Therefore, the “cold” type of hydrological conditions prevailed in the South Kuril area during August-November 2017. The surface water temperature was below the norm by 1–2 °C. On the contrary, the “warm” type of hydrological conditions prevailed in the South Kuril area during August-November 2018 and the water temperature in the area under consideration was 1–3 °C higher than the average for many years. Saury fishing in 2018, as in 2017, began in the second decade of August on the peripheral fronts of the Ask eddy and continued here until the second decade of September. At the end of September, the fishing area formed in the southwestern part of the EEZ of the Russian Federation and, unlike last year, it remained until the beginning of the third decade of October. The “warm” type of hydrological conditions causes this duration of the fishery. Saury moved outside the EEZ in late October. Fishing for sardines and mackerel began in mid-July 2018 and was carried out on the northern periphery of the eddy A’. However, at the end of October, unlike in 2017, fishing here practically stopped due to a decrease in the temperature drops at the peripheral fronts of the eddy caused by the high temperature of the surface waters of the Oyasio current. In late October — the first half of November in 2018, mackerel and sardine fished in high-gradient areas of the Northern Subarctic Front (NSAF) close to the eastern and southern borders of the Russian EEZ. During fishing season 2018, in contrast to the previous year, schools of sardines and mackerel remained much longer in the economic zone of Russia.

Infection of the Pacific saury Cololabis saira (Brevoort, 1856) (Teleostei: Beloniformes: Scomberesocidae) by Pennella sp. (Copepoda: Siphonostomatoida: Pennellidae) south of the Subarctic Front

The Pacific saury (Cololabis saira) is a fish of commercial importance subject to unpredictable epidemics of infection by Pennella sp., a parasitic copepod. We analyzed the distribution of fish presenting with newly attached Pennella to determine the region and season in which Pennella first infect the fish. Pacific sauries migrate northward in the spring to spend the summer in the subarctic region, successively crossing the Subarctic Boundary (SAB) and the Subarctic Front (SAF). The fish then return to subtropical waters in the fall and overwinter there. Pacific sauries infected with Pennella were observed on both the north and south sides of the SAF from May to December. Newly attached Pennella, however, were observed mainly to the south of the SAF during the northward migration of the fish in May and June, and only to the south of the SAB during the southward migration in November and December. These results indicate that the intermediate host or hosts of Pennella inhabit the region south of the SAF, with infection of Pacific saury occurring during late fall and spring. Such information may assist in identifying the intermediate host(s).

The recent AMOC variability in the Subpolar Gyre: results across the OVIDE section

<p><span>According to the subpolar AMOC index built from ARGO and altimetry, the AMOC amplitude across the OVIDE section (from Greenland to Portugal) was similar to that of the mid-1990s between 2014 and 2017, i.e. 4-5 Sv above the level of the 2000s. It then returned to average values in 2018. The same index computed independently from the biennial summer cruises over 2002-2018 confirms this statement. Interestingly, despite the concomitant cold and fresh anomaly in the subpolar Atlantic, the heat flux across OVIDE remains correlated with the AMOC amplitude. This can be explained by the paths taken by the North Atlantic Current and the transport anomalies in the subarctic front. In 2014, the OVIDE section was complemented by a section from Greenland to Newfoundland (GA01), showing how the water of the lower limb of the AMOC was densified by deep convection in the Labrador Sea. The spatial patterns of volume, heat, salt and oxygen transport anomalies after 2014 will be discussed at the light of the 2000s average.</span></p>

Pleistocene shifts of the Subarctic Front in the North Pacific: Evidence from planktonic foraminiferal proxy data

<p>The North Pacific plays a key role in shaping the Earth’s climate, yet there still is a lack in understanding the complex interplay of atmosphere and ocean, and their respective circulation patterns reacting to a varying Pleistocene climate. Proxy records established on marine sediment core SO264-28-2, recovered from the Emperor Seamount Chain (Suiko Seamount; ~45°N, close to the Subarctic Front) during R/V SONNE Cruise SO264 in 2018, allow to reconstruct changes of surface and subsurface water masses in order to provide unique insight in spatial and temporal shifts of North Pacific Subarctic<em> vs.</em> Subtropical gyres. According to the preliminary age model based on radiocarbon dating, benthic oxygen isotopes, combined magneto-, tephra- and biostratigraphical approaches, the only 7 m long core covers the last ~1.35 Myr. This core was chosen due to its highly characteristic pattern in magnetic susceptibility and a prominent lithological change from carbonate oozes to more siliciclastic sediment sequences at ~1.2 Ma. Thus, numerous other cores from the study area can be correlated with it suggesting this core as a reference record for the North Pacific.</p><p>A continuous and synchronous cooling of both surface and subsurface ocean temperatures since ~1.35 Ma changed rapidly at 1.2 Ma to a continuous warming surface from <4 °C to ~ 8 °C while subsurface temperature remained constant below 4 °C. The long-term diverging temperatures and increasing salinities at both surface and subsurface point to the continuous northward displacement of the Subarctic Front and an increased influence of the North Pacific Tropical Water at Suiko Seamount, with most prominent, millennial-scale, changes of the gyre system and the related Kuroshio Current during interglacials. Around ~430 ka, the influence of warm and saline subtropical surface water masses declines, reflected by a rapid decrease of sea surface temperatures of 4-5 °C and a salinity inversion, whereby the subsurface water mass becomes more saline than the surface water. After ~430 ka, interglacials are very pronounced and with the prominent presence of low saline and cooler surface waters, conditions are similar to present.</p>

LONG-TERM VARIABILITY OF CURRENTS IN THE SUBARCTIC FRONT OF THE ATLANTIC OCEAN

Based on time series of near-bottom current velocities and temperatures obtained in the period June, 2016 to July, 2017, at three points in the Atlantic Subarctic Front, along with the use of multi-year (since 1993 up to now) satellite ocean surface sounding data, multi-scale fluctuations of ocean surface and near-bottom flows over the western and eastern flanks of the Reykjanes ridge, as well as near Hatton Rise, on the Rokoll plateau, are studied. Hydrological profiles were carried out from the ocean surface to the bottom with readings every 10 m, when setting and retrieving the buoy stations. Using data from the Bank of hydrological stations (WOD13), SST satellite arrays (Pathfinder), long-term sea level and geostrophic velocities time series (AVISO), and bottom topography (model ETOPO-1), features of longterm cyclical fluctuations of SST, sea level, geostrophic currents on the ocean surface were defined in the sub-polar North Atlantic. It is shown that, in accordance with the large-scale thermohaline structure of the Subarctic front, two branches of the North Atlantic Current are detected on the ocean surface.One is directed from the Hatton towards the Icelandic-Faroese Rise, and the other – alomg the western flank of the Reykjanes Ridge toward Iceland. For the first branch, which is the main continuation of the North Atlantic Current, the average (for 25 years) water drift at a speed of 9.1±0.1 cm/s is determined to the northeast. The second branch, which forms the eastern part of the Subarctic cyclonic gyre, has the average water drift at a speed of 4.0±0.1 cm/s is directed north-northeast, along the western flank of the Reykjanes Ridge. In the intermediate waters of the frontal zone, an average water flow is observed at a speed of 2.7±0.1 cm/s to the north-northeast, along the eastern slope of the Reykjanes ridge.Due to the multy-scale components of the total variability, the average kinetic energy densities(KED) of total currents (109, 45, 97, (±3) erg/cm3, at station points from east to west) are much greater than the mean drift KED. The near-bottom flows on the Reykjanes ridge flanks are opposite to the direction of the North Atlantic Current. Outside the Subarctic gyre, the direction of average transport is maintained from the ocean surface to the bottom. The average (per year) KED of near-bottom currents are 31, 143, 27 (±3 erg/cm3), for three stations from east to west, respectively. In the intermediate waters of the frontal zone, above the eastern slope of the Reykjanes Ridge, there is a powerful reverse (relative to the North Atlantic Current) near-bottom water flow to the south-west, with a high average speed of ~ 15 cm/s. The KED of the currents during the year varies widely from zero to ~ 600 erg/cm3. The overall variability is due to cyclical variations and intermittency (“flashes”) of currents. Perennial cycles, seasonal variations, synoptic fluctuations with periods in the range of 30–300 days, as well as inertial oscillations and semi-diurnal tidal waves are distinguished. The intermittency of oscillations is partly due to changes in low-frequency flows, which can lead to a dopler frequency shift in the cyclic components of the spectrum. The amplitude of temperature fluctuations in the bottom layer for the year was (0.07–0.10) ± 0.01°C by the standard deviation. The seasonal changes of the bottom temperature are not detected. However, a linear trend with a warming of ~ (0.10–0.15) ± 0.01°С per year is noticeable.