Boreal Shelf Research Articles

High sensitivity of a keystone forage fish to elevated CO2 and temperature.

Sand lances of the genus Ammodytes are keystone forage fish in coastal ecosystems across the northern hemisphere. Because they directly support populations of higher trophic organisms such as whales, seabirds or tuna, the current lack of empirical data and, therefore, understanding about the climate sensitivity of sand lances represent a serious knowledge gap. Sand lances could be particularly susceptible to ocean warming and acidification because, in contrast to other tested fish species, they reproduce during boreal winter months, and their offspring develop slowly under relatively low and stable pCO2 conditions. Over the course of 2 years, we conducted factorial pCO2 × temperature exposure experiments on offspring of the northern sand lance Ammodytes dubius, a key forage species on the northwest Atlantic shelf. Wild, spawning-ripe adults were collected from Stellwagen Bank National Marine Sanctuary (Cape Cod, USA), and fertilized embryos were reared at three pCO2 conditions (400, 1000 and 2100 μatm) crossed with three temperatures (5, 7 and 10 ˚C). Exposure to future pCO2 conditions consistently resulted in severely reduced embryo survival. Sensitivity to elevated pCO2 was highest at 10 ˚C, resulting in up to an 89% reduction in hatching success between control and predicted end-of-century pCO2 conditions. Moreover, elevated pCO2 conditions delayed hatching, reduced remaining endogenous energy reserves at hatch and reduced embryonic growth. Our results suggest that the northern sand lance is exceptionally CO2-sensitive compared to other fish species. Whether other sand lance species with similar life history characteristics are equally CO2-sensitive is currently unknown. But the possibility is a conservation concern, because many boreal shelf ecosystems rely on sand lances and might therefore be more vulnerable to climate change than currently recognized. Our findings indicate that life history, spawning habitat, phenology and developmental rates mediate the divergent early life CO2 sensitivities among fish species.

Three new species of Thelepus Leuckart, 1849 from Europe and a re-description of T. cincinnatus (Fabricius, 1780) (Annelida, Terebellidae).

The review of a large amount of material previously identified as the terebellid annelid, Thelepus cincinnatus (Fabricius, 1780) shows that, within European waters from the Mediterranean to the North Pole, this species should be split into four species, three of which (T. davehalli sp. n., T. marthae sp. n., and T. parapari sp. n.) are newly described here and T. cincinnatus s. str. is re-described. These four species each show distinct distribution ranges. Thelepus cincinnatus has notopodia on almost all segments and numerous eyespots; it inhabits the high boreal and arctic shelf and the North Atlantic slope, and probably also occurs on the North Pacific shelf and slope. Thelepus marthae sp. n. has no eyespots and inhabits deep waters of the high Arctic. Thelepus davehalli sp. n. has no eyespots and has notopodia on 1/2 to 2/3 of the anterior of the body; it inhabits boreal shelf waters (from Iceland to the Mediterranean) below the tidal front. Thelepus parapari sp. n. differs from the previous three species in that the uncini of the first uncinigerous segment has two teeth above the main fang; it inhabits shallow, coastal waters of the Mediterranean, inshore from the tidal front.

Reworked Middle Jurassic sandstones as a marker for Upper Cretaceous basin inversion in Central Europe—a case study for the U–Pb detrital zircon record of the Upper Cretaceous Schmilka section and their implication for the sedimentary cover of the Lausitz Block (Saxony, Germany)

The Saxonian–Bohemian Cretaceous Basin (Elbsandsteingebirge, E Germany and Czech Republic, Elbtal Group) comprises Upper Cretaceous sedimentary rocks from Upper Cenomanian to Santonian age. These sandstones were deposited in a narrow strait of the sea linking the northern Boreal shelf to the southern Tethyan areas. They were situated between the West Sudetic Island in the north and the Mid-European Island in the south. As known by former studies (e.g. Troger, Geologie 6/7:717–730, 1964; Troger, Geologie von Sachsen, Schweizerbart, 311–358, 2008; Voigt and Troger, Proceedings of the 4th International Cretaceous Symposium, 275–290, 1996; Voigt, Dissertation, TU Bergakademie Freiberg, 1–130, 1995; Voigt, Zeitschrift der geologischen Wissenschaften 37(1-2): 15–39, 2009; Wilmsen et al., Freiberger Forschungshefte C540: 27–45, 2011) the main sedimentary input came from the north (Lausitz Block, southern West-Sudetic Island). A section of Turonian to Coniacian sandstones was sampled in the Elbsandsteingebirge near Schmilka (Elbtal Group, Saxony, Germany). The samples were analysed for their U–Pb age record of detrital zircon using LA-ICP-MS techniques. The results show main age clusters typical for the Bohemian Massif (local material) and are interpreted to reflect the erosion of uniform quartz-dominated sediments and basement rocks. Surprisingly, these rocks lack an expected Upper Proterozoic to Lower Palaeozoic age peak, which would be typical for the basement of the adjacent Lausitz Block (c. 540–c. 560 Ma). Therefore, the Lausitz Block basement must have been covered by younger sediments that acted as source rocks during deposition of the Elbtal Group. The sandstones of the Elbe valley (Elbtal Group, Schmilka section) represent the re-deposited sedimentary cover of the Lausitz Block in inverse order. This cover comprised Permian, Triassic, Jurassic and Lower Cretaceous deposits, which are eroded already today and cannot be investigated. Within the samples of the Elbtal Group (Schmilka section), the zircon age patterns change significantly towards the Lower Coniacian (topmost sample of the analysed section), where a major input of Meso- and Paleoproterozoic grains was obtained. Comparable ages are generally scarce in the working area. To have a reference for the detrital zircon age spectra of Triassic and Jurassic sediments of the area, two Upper Triassic und two Middle Jurassic clastic sediments of Germany were analysed. Surprisingly, the two Middle Jurassic (Dogger) sandstones from Bavaria and Lower Saxony showed similar detrital zircon age compositions as the Coniacian sediments on top of the Schmilka section (Elbe valley, Elbtal Group). In contrast, the two Upper Triassic sediments could be excluded as possible source rocks for the Upper Cretaceous sandstones of the Elbe valley (Schmilka section, Elbtal Group). The Meso- and Paleoproterozoic zircon age populations in the uppermost sandstone sample of the Schmilka section are assumed to originate from recycled Jurassic (Dogger) sandstones, resting on the Lausitz Block. These Middle Jurassic deposits were strongly influenced by a sedimentary input from the Scandinavian region (southern Baltica and North Sea Dome). The Turonian sandstones of the Schmilka section (samples below the topmost Coniacian sample) are interpreted to represent re-deposited Lower Cretaceous sediments resting on the Lausitz Block. A proposed synsedimentary uplift of about 5 km during the Upper Cretaceous along the Lausitz Fold (Lange et al., Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften 159(1):123–132, 2008) would have caused erosion of the pre-existing sedimentary cover of the Lausitz Block followed by inverse accumulation of the detritus into the Cretaceous Basin (Elbe valley, Elbtal Group). The Permian and Triassic cover units of the Lausitz Block were not exposed during the Upper Cretaceous, but are assumed to have contributed to younger (post-Coniacian) sediments of the Elbtal Group, which were eroded during uppermost Cretaceous and lower Paleogene. Based on this study, the detrital zircon record of the Jurassic Dogger sandstones of Germany can be seen as “marker ages” for the European Cretaceous Basin inversion. This paper presents the first results of a case study with further investigations in other areas of Europe to follow.

High-resolution Campanian–Maastrichtian carbon and oxygen stable isotopes of bulk-rock and skeletal components: palaeoceanographic and palaeoenvironmental implications for the Boreal shelf sea

AbstractA high-resolution latest Early Campanian to Early Maastrichtian carbon and oxygen stable isotope record from the northern German Boreal shelf sea based on 537 analyses of co-occurring belemnites, brachiopods, inoceramids, oysters, and bulk rock samples is presented. All samples are precisely related to their stratigraphic, systematic and facies backgrounds and form an integrated, nearly 10-myr-long dataset with considerable palaeoenvironmental and palaeoceanographical implications. Petrographic studies indicate that low-magnesium calcitic coccoliths and calcispheres (i.e., planktic carbonate) predominate the bulk-rock data (marl-limestone rhythmites and chalks), thus representing a sea-surface water signal, and that only minor diagenetic alteration of the carbonate muds took place. Based on TL and CL microscopy, the investigated belemnites are extraordinarily well preserved, which may in part be explained by their early diagenetic surficial silicification (container effect), while the other macroinvertebrate groups are all less well preserved. The (plankton-dominated) δ13C values of the marl-limestone rhythmites and chalks (+1.1 to +2.5 ‰), recording a surface water signal, compare well with the δ18C data of inoceramids while δ13Cbrach. values (+1.5 to +3.0 ‰) are heavier than the bulk rock data. The large variation in the δ13Cbel. (-0.1 to +3.6 ‰) is attributed to isotopic disequilibrium of the biogenic carbonate formed by the belemnite animal. The bulk rock δ18O values show a remarkable low scatter, supporting petrographic observation of only minor diagenetic stabilisation/cementation, and can be approximated with northern German shelf sea-surface temperatures of ca. 20°C for the Late Campanian (ca. -2 ‰ δ18O), being slightly cooler during the Early Maastrichtian. The δ18O values of the belemnite rostra are even less variable and quite rich in heavier18O (-0.7 to +0.6 with a mean of -0.1 ‰ δ18Obel.) in comparison to bulk rock and other skeletal components. Based on their excellent microstructural preservation and non-luminescence, we conclude that the belemnite rostra are diagenetically unaltered and have preserved the primary δ18O signal of ambient seawater (12 ± 2°C). In the absence of any indication for migration from cooler water masses and evidence for authochtonous populations we assume that the belemnites of the genera Belemnitella and Belemnella lived as nektobenthos near the sea-floor and thus record the temperature of the bottom mixed layer of the seasonally weakly stratified north German shelf sea at water depths of 100 to 150 m; the temperature gradient was thus 12.5-18.75 m/1°C. A conspicuous latest Campanian cooling event is evident in both sea-surface and bottom-water temperatures. The δ18O values of nearly all investigated benthic fossils lie between the isotope values of pristine belemnites and bulk rock, and, therefore, should be used for palaeotemperature reconstructions only with great care.

Climate effects on Barents Sea ecosystem dynamics

AbstractDalpadado, P., Ingvaldsen, R. B., Stige, L. C., Bogstad, B., Knutsen, T., Ottersen, G., and Ellertsen, B. 2012. Climate effects on Barents Sea ecosystem dynamics. – ICES Journal of Marine Science, 69: . Effects of climate variability and change on sea temperature, currents, and water mass distribution are likely to affect the productivity and structure of high-latitude ecosystems. This paper focuses on the Barents Sea (BS), a productive Arcto–boreal shelf ecosystem sustaining several ecologically and economically important fish species. The water masses in the region are classified as Atlantic, Arctic, and mixed, each having a distinct ecological signature. The pronounced increase in temperature and a reduction in the area covered by Arctic water that has taken place during the past decade have affected the ecology of the region. An increase in biomass of lipid-rich euphausiids in recent years, possibly linked to the temperature increase, has apparently provided good feeding and growth conditions for several species, including capelin and young cod. The observed reduction in Arctic zooplankton may on the other hand have negative implications for polar cod and other zooplankton predators linked to the Arctic foodweb. Despite these changes, the BS at present seems to maintain relatively stable levels of boreal zooplankton biomass and production, with no significant changes in the abundances of Calanus finmarchicus or the episodic immigrant C. helgolandicus.

Stable organic carbon isotope stratigraphy across Oceanic Anoxic Event 2 of Demerara Rise, western tropical Atlantic

Ocean Drilling Program (ODP) Leg 207 recovered expanded sections of organic‐carbon‐rich laminated shales on Demerara Rise (western tropical Atlantic). High‐resolution organic carbon isotope and total organic carbon (TOC) records are presented, which span the Cenomanian‐Turonian boundary interval (CTBI), including the Oceanic Anoxic Event (OAE) 2, from four sites oriented along a NW striking depth transect. These records represent the first high‐resolution carbon isotope records across OAE 2 from the South American margin of the tropical Atlantic. Due to the scarcity of age significant fossils, the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the CTBI across the depth transect and to tie this to biostratigraphically well‐defined sections in the Western Interior Basin (Pueblo, USA), boreal shelf seas (Eastbourne, England), and western Tethys (Oued Mellegue, Tunisia). All four sections studied document a 6‰ increase of δ13Corg values at the base of the CTBI, which is followed by an interval of elevated δ13Corg values and a subsequent decrease. Our results supply an important stratigraphic base for subsequent paleoceanographic studies on Late Cenomanian to Early Turonian sediments from Demerara Rise and elsewhere.

Fisheries in boreal ecosystems

Northern boreal shelf ecosystems are characterized by relatively few dominant species with strong interactions. The environment is highly dynamic, with strong impacts from oceanographic events that have major influences on fish stocks by altering recruitment, growth, and migration patterns. Excessive catches of one species may lead to the collapse of an important predator or prey in the system and may cause changes in the growth and survival patterns of other species in the food web. Four ecosystems – the Barents Sea/Norwegian Sea, the Bering Sea, the Iceland/Jan Mayen area, and the Newfoundland Shelf area – are compared and the impacts of climate and fishing are discussed on the basis of the recent literature. 2000 International Council for the Exploration of the Sea

Foraminiferal biozonation in the Early Pleistocene in the Central North Sea

Pliocene and Pleistocene deposits from 66 boreholes from the central and northern North Sea have been examined for their content of benthic foraminifera. In this area the Pliocene/Pleistocene boundary is generally placed at the bottom or middle of the Elphidium oregonense Subzone or at the last local occurrence of Cibicides grossus. A detailed study of the temporal relationship between these two species in the western part of the Danish sector shows, that the last local occurrence of Cibicides grossus in this area is older than the Elphidium oregonense Subzone. On the basis of the results concerning the Lower Pleistocene an emendation of the foraminiferal biostratigraphy for this sub-series is proposed and related to previous work on the biostratigraphy and palaeogeography of the North Sea area. The investigation indicates the existence of two distinct new subzones within the Elphidiella hannai/Cassidulina teretis range: The oldest of the two new subzones is an Acme-zone with Buliminidae as the characteristic taxon, and it is named the Stainforthia/Bulimina Subzone. The depositional environment was a boreal shelf with a water depth presumed to exceed 100 m. Based on its stratigraphic position and enviromental indications the Subzone is referred to the Tiglian stage. The youngest of the two new subzones is a local Range-zone, defined by the presence of the arctic species Elphidiella gorbunovi, and it is named the Elphidiella gorbunovi Subzone. The depositional environment was an arctic shelf with a water depth of less than 50 m. The occurrence of Elphidiella gorbunovi in the central North Sea thus indicates a cold interval in either the Eburonian or the Menapian stage. Succeeding the Elphidiella gorbunovi Subzone, the foraminiferal fauna and the sediment indicate increasingly near-coastal environment and a warming of the climate.

A review of the biogeography of cretaceous belemnites

A pattern of Boreal and Tethyan marine faunal realms was initiated in the Jurassic and continued into the Cretaceous. The belemnites first display this pattern in the Early Jurassic, and from the Middle Jurassic to earliest Cretaceous two morphologically distinct suborders, the Belemnitina and the Belemnopseina, were restricted to the boreal shelf seas and the Tethyan and Gondwanan shelf seas, respectively. An Austral marine realm was notably lacking during this interval. Significant change occurred in the late Barremian to early Aptian when the Belemnitina died out leaving the Belemnopseina, initially the Belemnopseidae, but followed by the Belemnitellidae, to invade their niches. An Austral Realm was initiated at this time, with the first appearance of a Gondwanan belemnopseine family, the Dimitobelidae. The Tethyan belemnite realm cannot be recognised after the Cenomanian, although the Belemnitellidae and Dimitobelidae defined Boreal and Austral belemnite realms throughout the Late Cretaceous. Climatic zonation remains the most often cited prime cause of provinciality in belemnites. However, examination of diversity patterns and faunal distributions reveals that palaeogeographic and palaeoceanographic factors were as important, if not more so, in determining Cretaceous provincial boundaries.