ALBERT

Description: The Observing Air–Sea Interactions Strategy (OASIS) is a new United Nations Decade of Ocean Science for Sustainable Development programme working to develop a practical, integrated approach for observing air–sea interactions globally for improved Earth system (including ecosystem) forecasts, CO2 uptake assessments called for by the Paris Agreement, and invaluable surface ocean information for decision makers. Our “Theory of Change” relies upon leveraged multi-disciplinary activities, partnerships, and capacity strengthening. Recommendations from 〉40 OceanObs’19 community papers and a series of workshops have been consolidated into three interlinked Grand Ideas for creating #1: a globally distributed network of mobile air–sea observing platforms built around an expanded array of long-term time-series stations; #2: a satellite network, with high spatial and temporal resolution, optimized for measuring air–sea fluxes; and #3: improved representation of air–sea coupling in a hierarchy of Earth system models. OASIS activities are organized across five Theme Teams: (1) Observing Network Design & Model Improvement; (2) Partnership & Capacity Strengthening; (3) UN Decade OASIS Actions; (4) Best Practices & Interoperability Experiments; and (5) Findable–Accessible–Interoperable–Reusable (FAIR) models, data, and OASIS products. Stakeholders, including researchers, are actively recruited to participate in Theme Teams to help promote a predicted, safe, clean, healthy, resilient, and productive ocean.

Description: The basalt stratigraphy of the Deccan Trap between Mahabaleshwar Ghat and Belgaum over-steps the basement from north to south. Sr-isotope and Zr/Nb ratios, and Sr, Rb, and Ba concentrations correlate portions of the post-Poladpur stratigraphy over 250 km along the Western Ghats, thereby confirming a southerly component of dip of 0·06°. At the southwestern margin, the stratigraphy extends upwards from the compositionally uniform Ambenali Formation (Cox & Hawkesworth, 1984) into a sequence of grossly heterogeneous flow units which have been allocated to the Mahabaleshwar and Panhala Formations (Lightfoot & Hawkesworth, 1988). The Mahabaleshwar Formation is represented only by a sequence of highly fractionated flows (termed the Kolhapur unit) with similar 87Sr/86Sr0 to the Mahabaleshwar (0·7045), but with Sr〈240 ppm and TiO2〉2·25%. Succeeding the Kolhapur unit are a series of flows with high 87Sr/86Sr0 (0·7045-0·705), Zr/Nb 〉 13, and low Sr (〈 200 ppm), which have been allocated to the Panhala Formation, and a group of flows with high 87Sr/86Sr0 (0·707–0·708) and Sr (〉230), but trace element concentrations similar to the Mahabaleshwar Formation; these have been allocated to the Desur unit of the Panhala. Geochemical variations in flows overlying the Ambenali define two distinct trends: one is attributed to gabbro fractionation, and the other to variations in the compositions of the parental magmas, and arguably their source regions. There is little evidence for significant crustal contamination in these flows, and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the Mahabaleshwar Formation. The high TiO2 content of Kolhapur unit flows is shown to be the result of shallow-level gabbro fractionation, rather than the presence of a primitive high-Ti magma. Mahabaleshwar Formation basalts exhibit a broad negative correlation between the degree of fractionation and Sr-isotopic composition. The endmember with lower 87Sr/86Sr0 has different Zr/Y from the Ambenali basalts, and would appear to have been generated by lower degrees of melting of a similar source. The other endmember has more radiogenic Sr, lower Zr/Nb, similar Zr/Y, but higher mg-number. The simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface, and that they then mixed to produce the Mahabaleshwar array. The Panhala Formation basalts plot on the Sr-Nd array defined by the Mahabaleshwar Formation, and the Desur unit basalts plot on an extension of this array; this suggests that the source characteristics are also lithospheric. The absolute elemental abundances may then be a function of melting and fractionation. We are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy, and suggest that this, together with the more protracted fractionation of the magma, reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice.

Description: In 1986 participants of the Benthos Ecology Working Group of ICES conducted a synoptic mapping of the infauna of the southern and central North Sea. Together with a mapping of the infauna of the northern North Sea by Eleftheriou and Basford (1989) this provides the database for the description of the benthic infauna of the whole North Sea in this paper. Division of the infauna into assemblages by TWINSPAN analysis separated northern assemblages from southern assemblages along the 70 m depth contour. Assemblages were further separated by the 30, 50 m and 100 m depth contour as well as by the sediment type. In addition to widely distributed species, cold water species do not occur further south than the northern edge of the Dogger Bank, which corresponds to the 50 m depth contour. Warm water species were not found north of the 100 m depth contour. Some species occur on all types of sediment but most are restricted to a special sedimentand therefore these species are limited in their distribution. The factors structuring species distributions and assemblages seem to be temperature, the influence of different water masses, e.g. Atlantic water, the type of sediment and the food supply to the benthos. Eleftheriou, A. and Basford, D. J. Journal of the Marine Biological Association of the UK, 69: 123–143.

Description: Oithona similis is an abundant but poorly studied cyclopoid copepod in the brackish Central Baltic Sea. We describe the spatio-temporal distribution of O. similis in a Central Baltic deep basin (Bornholm Basin) during spring and summer 1999. Using vertically resolving sampling in parallel with hydrographic measurements, we found the copepod to dwell in the permanent halocline characteristic of a Central Baltic deep basin. The habitat of O. similis is thus limited from above by low salinity and from below by low oxygen conditions, both characteristic for the area. Horizontally resolving sampling yielded abundance surfaces which were compared by analysis of variance showing similar patterns among sampling dates. Comparison with flow fields from a three-dimensional hydrodynamic model suggests that the horizontal distribution is primarily the result of circulation in the dwelling depth. The study shows how the physical environment in the area determines the spatial distribution which might affect abundance and production of this copepod.

Description: Environmentally induced change appears to be impacting the recruitment of North Sea herring (Clupea harengus). Despite simultaneously having a large adult population, historically low exploitation, and Marine Stewardship Council accreditation (implying sustainability), there have been an unprecedented 6 sequential years of poor juvenile production (recruitment). Analysis suggests that the poor recruitment arises during the larval overwintering phase, with recent survival rates greatly reduced. Contemporary warming of the North Sea has caused significant changes in the plankton community, and a recently identified regime shift around 2000 shows close temporal agreement with the reduced larval survival. It is, therefore, possible that we are observing the first consequences of this planktonic change for higher trophic levels. There is no indication of a recovery in recruitment in the short term. Fishing mortality is currently outside the agreed management plan, and forecasts show a high risk of the stock moving outside safe biological limits soon, potentially precipitating another collapse of the stock. However, bringing the realized fishing mortality back in line with the management plan would likely alleviate the problem. This illustrates again that recruitment is influenced by more than just spawning-stock biomass, and that changes in other factors can be of equal, or even greater, importance. In such dynamically changing environments, recent management success does not necessarily guarantee future sustainability.

Description: Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits.

Description: The Nifonea submarine volcano rises 1000 m above the seafloor of the Vate Trough back-arc basin behind the New Hebrides island arc. This large volcanic edifice has a caldera of ∼8 km diameter and is connected to two ∼20 km long volcanic rift zones in the back-arc basin. We present new chemical and isotope data for volcanic glasses and whole-rocks from both the volcano and its rift zones. Lavas from Nifonea volcano show an evolution towards more incompatible element enrichment, with the most enriched lavas being the youngest eruption products on the caldera floor. These are products of significant fractional crystallization, show minor contamination by hydrothermal fluids (〈0·3%) and reflect mixing of melts derived from depleted upper mantle and melts from an enriched source similar to those occurring in the North Fiji Basin. The enrichment in Nb of these lavas is comparable with that of some lavas from the New Hebrides island arc (e.g. Mota Lava island), where these coexist with typical island arc basalts. The lavas erupted along the rift zones in the Vate Trough back-arc basin are relatively depleted in incompatible elements, indicating melting of depleted upper mantle with a minor addition of a sediment-derived fluid. Our observations suggest that the mantle beneath Vate Trough is heterogeneous on a small scale (〈20 km) and that the occurrence of these enriched and fertile mantle portions has a stronger control on melting processes than the influx from the subducting slab, as all samples were recovered at a similar distance from the trench.

Description: This study presents a new method (LBB) for the analysis of length frequency data from commercial catches. LBB works for species that grow throughout their lives, such as most commercially-important fish and invertebrates, and requires no input in addition to length frequency data. It estimates asymptotic length, length at first capture, relative natural mortality, and relative fishing mortality. Standard fisheries equations can then be used to approximate current exploited biomass relative to unexploited biomass. In addition, these parameters allow the estimation of length at first capture that would maximize catch and biomass for a given fishing effort, and estimation of a proxy for the relative biomass capable of producing maximum sustainable yields. Relative biomass estimates of LBB were not significantly different from the “true” values in simulated data and were similar to independent estimates from full stock assessments. LBB also presents a new indicator for assessing whether an observed size structure is indicative of a healthy stock. LBB results will obviously be misleading if the length frequency data do not represent the size composition of the exploited size range of the stock or if length frequencies resulting from the interplay of growth and mortality are masked by strong recruitment pulses.

Description: Total biomass and biomass of large taxonomic groups (polychaetes, molluscs, crustaceans, echinoderms) and species diversity of the macrofauna were determined for almost 200 North Sea stations sampled synoptically by seven vessels during Spring 1986 and for 120 additional stations sampled in earlier years by the Marine Laboratory in Aberdeen. There exists a clear and significant decreasing trend in biomass with latitude, both in total biomass and for the different taxonomic groups. Apart from latitude, sediment composition and chlorophyll a content of the sediment also infuence total biomass and biomass of most groups significantly. Biomass increases consistently in finer sediments and sediments with a higher chlorophyll a content. The same trends are found for the results within laboratories. Some interaction exists, indicating weak laboratory and zonal effects. Diversity, as measured by Hill's diversity index N1 = (exp H′) shows a clear and significant trend with latitude. Towards the north of the North Sea diversity increases considerably. The trend is also found for laboratories separately and is everywhere equally strong. Also longitude and depth show an effect on diversity. Sediment variables have no clear influence on diversity. Other diversity measures show the same trend but are more variable than N1,. Total density tends to increase towards the north, but sediment related variables have a larger influence. Mean individual weight becomes considerably smaller towards the northern part of the North Sea.

Description: Post-collisional magmatism in the southern Iberian and northwestern African continental margins contains important clues for the understanding of a possible causal connection between movements in the Earth's upper mantle, the uplift of continental lithosphere and the origin of circum-Mediterranean igneous activity. Systematic geochemical and geochronological studies (major and trace element, Sr–Nd–Pb-isotope analysis and laser 40Ar/39Ar-age dating) on igneous rocks provide constraints for understanding the post-collisional history of the southern Iberian and northwestern African continental margins. Two groups of magmatic rocks can be distinguished: (1) an Upper Miocene to Lower Pliocene (8·2–4·8 Ma), Si–K-rich group including high-K (calc-alkaline) and shoshonitic series rocks; (2) an Upper Miocene to Pleistocene (6·3–0·65 Ma), Si-poor, Na-rich group including basanites and alkali basalts to hawaiites and tephrites. Mafic samples from the Si–K-rich group generally show geochemical affinities with volcanic rocks from active subduction zones (e.g. Izu–Bonin and Aeolian island arcs), whereas mafic samples from the Si-poor, Na-rich group are geochemically similar to lavas found in intraplate volcanic settings derived from sub-lithospheric mantle sources (e.g. Canary Islands). The transition from Si-rich (subduction-related) to Si-poor (intraplate-type) magmatism between 6·3 Ma (first alkali basalt) and 4·8 Ma (latest shoshonite) can be observed both on a regional scale and in individual volcanic systems. Si–K-rich and Si-poor igneous rocks from the continental margins of southern Iberia and northwestern Africa are, respectively, proposed to have been derived from metasomatized subcontinental lithosphere and sub-lithospheric mantle that was contaminated with plume material. A three-dimensional geodynamic model for the westernmost Mediterranean is presented in which subduction of oceanic lithosphere is inferred to have caused continental-edge delamination of subcontinental lithosphere associated with upwelling of plume-contaminated sub-lithospheric mantle and lithospheric uplift. This process may operate worldwide in areas where subduction-related and intraplate-type magmatism are spatially and temporally associated.