Holocene Paleoceanography Research Articles

Holocene paleoceanography and glacial history of Lincoln Sea, Ryder Glacier, Northern Greenland, based on foraminifera and ostracodes

We reconstructed Holocene paleoceanography of the Sherard Osborn Fjord (SOF), N Greenland, and Lincoln Sea in the eastern Arctic Ocean using sediment properties and micropaleontology from cores obtained during the Ryder 2019 Expedition. Our aims were to better understand faunal indicators of water mass influence on Ryder Glacier and the Lincoln Sea at water depths >500 m. Benthic microfaunal reflect glacio-marine interval during late deglaciation ~10.5 to 8.5 ka (kiloannum) during the Holocene Thermal Maximum (HTM) with dominant benthic foraminiferal species Cassidulina neoteretis, Cassidulina reniforme, and the ostracode Rabilimis mirabilis. Casssidulina neoteretis is considered an indicator of Atlantic Water (AW) throughout the Arctic Ocean and Nordic Seas; C. reniforme reflects glacio-marine conditions from the retreating Ryder Glacier. Deglaciation was followed by a period of elevated productivity and diverse ostracode faunal assemblages that suggest AW influence from 8.5 to 6 ka in the Lincoln Sea and inside SOF. The Holocene occurrence of the ostracode species Acetabulastoma arcticum, that appears in low numbers in the Lincoln Sea and briefly (~ 4–3 ka) in SOF, reflects the presence of variable sea ice in this region. Based on the similarities of the Lincoln Sea and fjord ostracodes to modern and glacial-deglacial faunas from the central Arctic Ocean, the AW influence likely originates from recirculation of AW water from the central Arctic Basin. In general, our results suggest a strong but temporally varying influence of AW during the entire 10.5 kyr record of the Lincoln Sea and SOF.

Last Glacial Maximum to Holocene paleoceanography of the northwestern Ross Sea inferred from sediment core geochemistry and micropaleontology at Hallett Ridge

Abstract. During the Late Pleistocene–Holocene, the Ross Sea Ice Shelf exhibited strong spatial variability in relation to the atmospheric and oceanographic climatic variations. Despite being thoroughly investigated, the timing of the ice sheet retreat from the outer continental shelf since the Last Glacial Maximum (LGM) still remains controversial, mainly due to a lack of sediment cores with a robust chronostratigraphy. For this reason, the recent recovery of sediments containing a continuous occurrence of calcareous foraminifera provides the important opportunity to create a reliable age model and document the early deglacial phase in particular. Here we present a multiproxy study from a sediment core collected at the Hallett Ridge (1800 m of depth), where significant occurrences of calcareous planktonic and benthic foraminifera allow us to document the first evidence of the deglaciation after the LGM at about 20.2 ka. Our results suggest that the co-occurrence of large Neogloboquadrina pachyderma tests and abundant juvenile forms reflects the beginning of open-water conditions and coverage of seasonal sea ice. Our multiproxy approach based on diatoms, silicoflagellates, carbon and oxygen stable isotopes on N. pachyderma, sediment texture, and geochemistry indicates that abrupt warming occurred at approximately 17.8 ka, followed by a period of increasing biological productivity. During the Holocene, the exclusive dominance of agglutinated benthic foraminifera suggests that dissolution was the main controlling factor on calcareous test accumulation and preservation. Diatoms and silicoflagellates show that ocean conditions were variable during the middle Holocene and the beginning of the Neoglacial period at around 4 ka. In the Neoglacial, an increase in sand content testifies to a strengthening of bottom-water currents, supported by an increase in the abundance of the tycopelagic fossil diatom Paralia sulcata transported from the coastal regions, while an increase in ice-rafted debris suggests more glacial transport by icebergs.

Late Holocene paleoceanography in the Chukchi and Beaufort Seas, Arctic Ocean, based on benthic foraminifera and ostracodes

Calcareous microfossil assemblages in late Holocene sediments from the western Arctic continental shelf provide an important baseline for evaluating the impacts of today’s changing Arctic oceanography. This study compares 14C-dated late Holocene microfaunal assemblages of sediment cores SWERUS-L2-2-PC1, 2-MC4 and 2-KL1 (57 mwd), which record the last 4200 years in the Herald Canyon (Chukchi Sea shelf), and HLY1302-JPC-32, GGC-30, MC-29 (60 mwd), which record the last 3000 years in the Beaufort Sea shelf off the coast of Canada. Foraminiferal and ostracode assemblages are typical of Arctic continental shelf environments with annual sea-ice cover and show relatively small changes in terms of variability of dominant species. Important microfaunal changes in the Beaufort site include a spike in Spiroplectammina biformis coinciding with a decrease in Cassidulina reniforme in the last few centuries suggesting an increase of Pacific Water influence and decreased sea-ice. There is low-amplitude centennial-scale variability in proportions of benthic foraminiferal species, such as C. reniforme. In addition to these species, Cassidulina teretis s.l., Elphidium excavatum clavatum and Stainforthia feylingi are also common at this site. At the Herald Canyon site in the last few centuries, C. reniforme peaks around 150 years BP and then decreases while Spiroplectammina earlandi spikes and Acanthocythereis dunelmensis decreases also suggesting an increase in Pacific Water influence and decreased sea-ice at this site. This site also includes Buccella spp. and Elphidium excavatum clavatum. Differences in benthic foraminifera and ostracode species dominance between the two sites may be due to a greater influence of Pacific Water in the Chukchi shelf, compared to the more distal Beaufort shelf, which is also affected by the Beaufort Gyre and the Mackenzie River.

Holocene paleoceanography of Bigo Bay, west Antarctic Peninsula: Connections between surface water productivity and nutrient utilization and its implication for surface-deep water mass exchange

Paleoceanographic changes in response to Holocene climate variability in Bigo Bay, west Antarctic Peninsula (WAP) were reconstructed through geochemical, isotopic, sedimentological, and microfossil analysis. Core WAP13-GC47 is composed of 4 lithologic units. Unit 4 was deposited under ice shelf settings. Unit 3 represents the mid-Holocene open marine conditions. Unit 2 indicates lateral sediment transport by a glacier advance during the Neoglacial period. The chronological contrast between the timing of open marine conditions at core WAP13-GC47 (ca. 7060 cal. yr BP at 540 cm) and the ages of calcareous shell fragments (ca. 8500 cal. yr BP) in Unit 2b suggests sediment reworking during the Neoglacial period. Unit 1 was deposited during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Surface water productivity, represented by biogenic opal and total organic carbon (TOC) concentrations, increased and bulk δ15N (nitrate utilization) decreased during the warmer early to middle Holocene and the MWP. In contrast, surface water productivity decreased with increased bulk δ15N during the colder Neoglacial period and LIA in Bigo Bay. The nitrate utilization was enhanced during cold periods in association with strong surface water stratification resulting from increased sea ice meltwater discharge or proximity to an ice shelf calving front in Bigo Bay. Reduced nitrate utilization during warm periods is related to weak stratification induced by less sea ice meltwater input and stronger Circumpolar Deep Water influence.

Holocene paleoceanography of the Bay of Biscay: Evidence for west-east linkages in the North Atlantic based on dinocyst data

Paleoceanographical changes during the Holocene were reconstructed from the study of core MD95-2002 situated in the northern Bay of Biscay, which is marked by the direct influence of the northeastern return branch of the North Atlantic Drift. Palynological data, sea-surface condition estimates based on dinocyst assemblages and stable isotope measurements in planktic and benthic foraminifera reveal a strong influence of freshwater/meltwaters from both the proximal European sources and the more distal Laurentide Ice Sheet, which experienced delayed deglaciation. The data also indicate the setting of a climate optimum between 7 and 5.5ka followed by a cooling trend, which is consistent with insolation changes and other regional records of climate changes. Superimposed on the long term trends, the reconstructions of sea-surface conditions evidence large amplitude changes at centennial to millennial time-scales, with seven episodes of cooling and low salinity since 11ka that generally match episodes of dense sea-ice cover in the Labrador Sea. The west to east transfer of the sea-ice and/or meltwater signal across the North Atlantic evidenced from core MD95-2002 points to strong linkages between western and eastern North Atlantic, probably in relation to the North Atlantic Oscillation (NAO) mode of variability.

Late Holocene paleoceanography and climate variability over the Mackenzie Slope (Beaufort Sea, Canadian Arctic)

Late Holocene paleoceanography and climate variability of the Southeastern Beaufort Sea (Canadian Arctic) have been investigated on the basis of sedimentary cores collected over the Mackenzie Slope. Piston, trigger and box cores were sampled at station 803 in 2004 aboard the CCGS Amundsen at 218m water depth. The chronology of the piston core is constrained by 4 AMS-14C dates, as the sedimentation rate in the box core is assessed from 210Pb data. We obtain a continuous composite sequence covering the last 4600years, with a sedimentation rate of ~140cm.kyr−1. Transfer functions (modern analogue technique) based on dinoflagellate cyst (dinocyst) assemblages were used to reconstruct the evolution of sea-surface conditions over the time period covered by the cores.Palynological data reveal that dinocyst assemblages are dominated by Operculodinium centrocarpum sensu lato (mean of 43.3%) throughout the core, with the accompanying taxa Brigantedinium spp. (19.6%), Islandinium minutum (15.6%) and cysts of Pentapharsodinium dalei (13.7%). Four zones have been established on the basis of dinocyst relative abundances. Dinocyst assemblage zone 1 (D1), from 4600 to 2700cal years BP, is dominated by O. centrocarpum (mean of 49.0%). In zone D2 (2700–1500cal years BP), the relative abundances of O. centrocarpum decrease (34.4%) in favour of the opportunistic, heterotrophic taxa Brigantedinium spp. (28.8%) and cysts of Polykrikos sp. var. arctic/quadratus (2.8%). Dinocyst zone D3 (1500–30cal years BP or 450–1920AD) is characterised by the high relative abundance of the peridinioid taxa I. minutum (19.9%). The last zone (D4), spanning from 1920 to 2004AD, is again dominated by O. centrocarpum (44.5%), and shows low relative abundances of Brigantedinium spp. and cf. Echinidinium karaense.Quantitative reconstructions of past sea-surface parameters (August sea-surface temperature: SST, August sea-surface salinity: SSS, and duration of sea-ice cover) indicate relatively stable conditions over the last 4.6kyr, with episodic cooling events (SST of ~1.5°C below the modern value of 6°C) that took place between 700 and 1820AD. We associate the last and the longest of these cooling events (1560–1820AD) with the Little Ice Age. Reconstructed SSS shows decadal oscillations since 1920AD that we tentatively associate with the accumulation of freshwater by the Beaufort Gyre and the subsequent Great Salinity Anomalies. Our data suggest that similar salinity anomalies could have occurred ca. 1860 and 1790AD.Stable isotopic data show a slight increase in δ13C values (from ~−27.1‰ at the base to ~−25.8‰ at the top) over the last 4.6kyr that we associate with the gradual increase in atmospheric CO2 concentration as recorded by Antarctic ice cores. Variations in the δ15N profile suggest variations in Pacific water influence from 4600 to ~1300cal years BP, associated with centennial scale shifts of the Arctic Oscillation phases.

Holocene paleoceanography of the northwest passage, Canadian Arctic Archipelago

A series of cores (box and piston) were collected at 2 key locations in Lancaster Sound (cores 2004-804-009 BC and PC) and Barrow Strait (cores 2005-804-004 BC and PC) in the Canadian Arctic Archipelago to document the evolution of sea-surface conditions in the main axis of the Northwest Passage during the Holocene time period. Reconstruction of sea-surface parameters (summer temperature and salinity, duration of sea-ice cover) were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators. The chronology of these cores is based on calibrated AMS- 14C dates, 210Pb analyses, and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field (CALS7 K.2). Our age models for both cores indicate that 009 PC spans the last 11,100 cal BP, while 004 PC encompasses the last 10,800 cal BP. Calculated sedimentation rates are in the range of 43–140 cm/kyr for core 009 PC and 15–118 cm/kyr for core 004 PC, allowing for a millennial time scale resolution in each core. Our results indicate relatively harsh conditions in Lancaster Sound between 10,800 and 9000 cal BP (summer temperatures 2 °C cooler than at present), which we associate with the presence of active ice-streams in northernmost Baffin Bay and a weak West Greenland Current. This is followed by a warming trend (up to 3 °C higher than present) that took place between ∼8500 and 5500 cal BP, which we associate with the Holocene thermal maximum and to a large scale atmospheric pattern such as the Arctic Oscillation operating at the millennial time scale. This is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa. A gradual cooling of sea-surface temperature and increased sea-ice follow this from 5500 cal BP until the modern period. In Barrow Strait, harsh sea-surface conditions prevailed from 11,100 to 5500 cal BP, with summer temperatures as low as 4 °C cooler than at present. The warming trend occurred later in this region (between 5500 and ∼1000 cal BP), after which a gradual cooling is observed until the modern period. The apparent shift, or opposite warming trends, between Lancaster Sound and Barrow Strait after 5500 cal BP could be the result of a change in atmospheric circulation patterns related to a possible shift in the AO mode (from AO + to AO −). Comparison of ice core δ 18O record from Devon Island ice cap and the reconstructed sea-surface temperature from core 009 PC suggests a strong atmospheric-oceanic coupling throughout the Holocene in this area.

The timing and evolution of the post-glacial transgression across the Sea of Marmara shelf south of İstanbul

High-resolution seismic reflection profiles and analyses of the sedimentary substrate at the Sea of Marmara (SoM) entrance to the Strait of İstanbul (SoI, Bosphorus) provide a detailed record of the transgression that took place after the SoM reconnected with the Mediterranean. The sediments progressively fill a paleo shelf valley that incised the margin from the SoI to the shelf break at the time of the pre-Holocene lowstand. We map seven seismic reflection units that can be confidently correlated to sediment cores by lithology and physical properties. Sediments in the cores are dated by radiocarbon methods. Early channel and levee deposits within the paleo valley belong to the Younger Dryas cold stage and record outflow from the Black Sea via the SoI. Small clinoform packages on the valley margin formed in proximity to climbing paleo shorelines. The elevations of these deposits conform to the sealevel history recorded in Barbados corals. The younger part of the succession includes a subaqueous prodelta sourced from the Kurbağalıdere River. Its relatively young age when the Holocene sea had almost reached its modern level suggests that the thick progradational and aggradational clinoform development was primarily a response to sediment supply rather than the filling of expanding accommodation space. Our findings refute the hypothesis of Aksu et al. (Aksu, A.E., Hiscott, R.N., Mudie., P.J., Rochon, A., Kaminski, M.A., Abrojano, T., Yaşar, D., 2002a. Persistent Holocene outflow fromn the Black Sea to the Eastern Mediterranean contradicts Noah's Flood hypothesis, GSA Today 10,(6), 3–7., Aksu, A.E., Hiscott, R.N., Kaminski, M.A., Mudie, P.J., Gillespie, H., Abrojano, T., Yaşar, D., 2002b. Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence. Mar. Geol., 190, 119–149.) and Hiscott et al. (Hiscott, R.N., Aksu, A.E., Yaşar, D., Kaminski, M.A., Mudie, P.J., Kostylev, V.E., MacDonald, J.C. Isler, F.I., Lord, A.R., 2002. Deltas south of the Bosphorus Strait record persistent Black Sea outflow to the Marmara Sea since ∼ 10 ka, Mar. Geol., 190, 95–118., Hiscott, R.N., Aksu, A.E., Mudie., P.J., Kaminski, M.A., Abrajano, T., Yaşar, D., Rochon, A., 2007. The Marmara Sea gateway since ∼ 16 ky BP: non-catastrophic causes of paleoceanographic events in the Black Sea at 8.4 and 7.15 ky BP. In Yanko-Hombach,V., Gilbert, A.S., Dolukhanov, P.M. (Eds.), The Black Sea Flood Question, Springer, The Netherlands, 89–117.) that this deposit was supplied from the SoI and that its presence requires a persistent Black Sea outflow since 10 14C ka bp (not corrected from the reservoir age or calibrated).

Late Glacial and Holocene paleoceanography in the Skagerrak from high-resolution grain size records

High-resolution grain size analyses of the AMS 14C-dated, 32 m long core MD99-2286 from the northeastern Skagerrak were performed in order to study late Glacial and Holocene paleoceanographic and sedimentary changes. All ages in this study are given in calibrated thousand years before present (= AD 1950), abbreviated ‘kyr’, unless otherwise noted. The distinct ending of IRD (ice rafted debris) in core MD99-2286, which was retrieved from a location down current from the final calving ice margin in the region, indicates that iceberg calving in the Skagerrak ended between 10.6 and 10.2 kyr. A clay-rich sequence in core MD99-2286, deposited between 11.3 and 10.3 kyr, is attributed to outflow from the Baltic basin across south central Sweden. The sequence is correlated to similar units from cores along the Swedish west coast. The onset of this clay-rich deposition occurs progressively later in cores further south along the coast, supporting a previous hypothesis that differential glacio-isostatic uplift caused a southward migration of the Baltic outflow from the Otteid-Stenselva to the Göta Älv outlet. A distinct coarsening towards younger sediments in core MD99-2286 indicates a hydrographic shift at 8.5 kyr, which is correlated to a shift previously reported in the Skagerrak, Kattegat and the Norwegian Channel. This shift reflects the establishment of the modern circulation system in the eastern North Sea, as a consequence of the opening of the English Channel and the Danish straits and increased Atlantic water inflow, and the subsequent development of the South Jutland Current. A general trend of coarsening, poorer sorting and increasing variability from 8.5 kyr until the present indicates increasing strength and influence of the variable South Jutland Current. A series of changes from ca. 6.3 to ca. 3.8 kyr in core MD99-2286 reflects strengthening of the Jutland Current towards the present day sedimentation system in the Skagerrak–Kattegat. These changes are correlated to previously reported hydrographic shifts at 5.5 14C years BP in the Skagerrak and at 4.0 14C years BP in the Kattegat. It is suggested that these shifts were separate features of a transitional period related to strengthening of the current system. The resulting changes are differently manifested in different parts of the Skagerrak–Kattegat, due to the complex circulation system. The last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material, reflecting a circulation system significantly modified by regional climatic conditions, especially the general wind directions and storm frequency over the southern North Sea.

Size-dependent isotopic composition of planktic foraminifers from Chukchi Sea vs. NW Atlantic sediments—implications for the Holocene paleoceanography of the western Arctic

In Arctic and sub Arctic seas, shell growth and/or secondary calcite overgrowth of Neogloboquadrina pachyderma (left coiled)—Npl—occur along the pycnocline, and their δ 13C and δ 18O-values are size and weight dependent. However, whereas the Npl 18O data from the NW Atlantic indicate near-equilibrium conditions with ambient waters and a positive relationship between shell weight and 18O-content, assemblages from box-cored sediments of the Chukchi Sea (western Arctic) are depleted by ∼2‰ with respect to equilibrium values with modern conditions, and depict a negative relationship between shell weight and its δ 18O-value (−0.15±0.03‰/μg on VPDB scale). A similar feature is also depicted by the dextral form of N. pachyderma (Npd). We associate the reverse shell-size or weight vs. δ 18O relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer, and the underlying near 3°C-warmer saline North Atlantic water mass. The analysis of two late to post-glacial sedimentary sequences from the Chukchi Sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the Holocene, thus reflecting an early onset of the modern-like linkage between the Arctic Ocean and the North Atlantic. Moreover, lower δ 18O-values in both Npl and Npd together with larger δ 18O-gradients between the different shell sizes at ca 9–7 ka BP suggest ∼3°C higher temperatures in the upper North Atlantic water mass, in comparison with the present (approximately +1°C, at the study site), thus likely a higher inflow rate of this water mass during the early Holocene.

High resolution Holocene palynological record from the Scotian Shelf

Because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold Labrador Current and the Gulf Stream, the Atlantic Provinces experience some of the most dynamic climate conditions in Canada. Major climate changes occurred during the Holocene, as shown by pollen records from lakes, but previous paleoceanographic studies, based on low-resolution proxy-data records do not show major changes during the past 8000 years. Therefore, the Holocene history of Canada's Atlantic region was examined using a high-resolution palynological record from the Scotian Shelf (La Have Basin). Sea surface conditions were reconstructed using proxy-data from dinoflagellate cysts and paleobioclimatic transfer functions. Ocean–atmosphere interactions are determined by onshore–offshore correlation of marine and pollen records from Nova Scotia. Results show a succession of major paleoceanographic events. Sea surface temperatures (SST) (February and August) up to 5°C higher than today's average and slightly higher salinity are reconstructed between 10.5 and 8.5 ka. The last pulse of meltwater from the residual ice sheet affected the shelf waters between 8.5 and 6.5 ka by lowering the SST (in February) and the salinity. Most previous studies failed to record this event. Since 6.5 ka, August temperature generally remained around today's value, while February temperature was generally 2°C above it, except for recurring colder and lower salinity intervals. These cold intervals have a recurrence of about 1000 years. A slight cooling of summer SST is recorded in the last 500 years. Comparison with climatic reconstructions from Nova Scotia pollen records shows a difference in timing between ocean and atmosphere. The onset of the climatic optimum (hypsithermal) in Nova Scotia lags by about 2000 years (until 8 ka) relative to the ocean but it lasted longer. The Neoglacial cooling in Atlantic Canada however, started earlier (2 ka) than the late Holocene ocean cooling. La Have Basin's Holocene paleoceanography presents some differences from most other studies from the region: (1) the hypsithermal started earlier; (2) the last pulse of meltwater is recorded; (3) the last 6500 years are punctuated by colder intervals. Increased productivity and blooms of toxic algae in the early Holocene are probably due to a combination of factors: increased nutrients and a greater stability of the water column because of meltwaters, higher SST and increased upwelling or storm activity.

Holocene paleoceanography in the southeast Venezuela Basin, Caribbean Sea

Abundance variations of benthic foraminifera in four box cores (3775–4447 m water depth) from the southeastern Venezuela Basin reflect the Holocene paleoclimatic history of the basin. There are no significant but some subtle paleoclimaticl changes during the Holocene. Overall, the following nine dominant calcareous benthic foraminifera species fluctuate down-core but display no obvious stratigraphic trends:Cibicides wuellerstorfi, Nuttallides decorata, Eponides polius, E. turgidus, E. tumidulus, Pullenia quinqueloba, P. bulloides, Melonis pompilioides, andOridorsalis tener. Primitive species of arenaceous foraminifera are abundant, while more complex forms are rare. Arenaceous foraminifera disappear at 16–18 cm depth in all four cores suggesting that below 16–18 cm the sediment is affected by diagenesis. Significant down-core dissolution of carbonate is seen in the deepest core 68-8 (4447 m). Except core 68-8, the late Holocene is characterized by a higher abundance of theGloborotalia menardii complex, a higher percentage of calcium carbonate, and a greater coarse fraction. Relatively large values for both calcium carbonate and coarse fraction percentages are caused by high productivity in warm surface waters. The late Holocene record of the foraminifera shows greater calcium carbonate dissolution, higher productivity (fertility), and more efficient water mixing during deposition than the early Holocene record. Corrosive bottom water masses are also indicated in the late Holocene by brown color and a high degree of broken planktonic foraminifera. The homogeneity of the southeastern Venezuela basin water mass is responsible for the small variations of S, H(S), and E.

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Foraminiferal assemblages were studied in northern Barents Sea core ASV 880 along with oxygen and carbon isotope measurements in planktonic (N. pachyderma sin.) and benthic (E clavatum) species. AMS C‐14 measurements performed on molluscs Yoldiella spp. show that this core provides a detailed and undisturbed record of Holocene climatic changes over the last 10000 calendar years. Surface and deep waters were very cold (<0°C) at the beginning of the Holocene. C. reniforme dominated the highly diverse benthic foraminiferal assemblage. From 10 to 7.8 cal. ka BP, a warming trend culminated in a temperature optimum, which developed between 7.8 and 6.8 cal. ka BP. During this optimum, the input of Atlantic water to the Barents Sea reached its maximum. The Atlantic water mass invaded the whole Franz Victoria Trough and was present from subsurface to the bottom. No bottom water, which would form through rejection of brine during winter, was present at the core depth (388 m). The water stratification was therefore greatly reduced as compared to the present. An increase in percentage of I. helenae/norcrossi points to long seasonal ice‐free conditions. The temperature optimum ended rather abruptly, with the return of cold polar waters into the trough within a few centuries. This was accompanied by a dramatic reduction of the abundance of C. reniforme. During the upper Holocene, the more opportunistic species E. clavatum became progressively dominant and the water column was more stratified. Deep water in Franz Victoria Trough contained a significant amount of cold Barents Sea bottom water as it does today, while subsurface water warmed progressively until about 3.7 cal. ka BP and reached temperatures similar to those of today. These long‐term climatic changes were cut by several cold events of short duration, in particular one in the middle of the temperature optimum and another, which coincides most probably with the 8.2 ka BP cold event. Both long‐ and short‐term climatic changes in the Barents Sea are associated with changes in the flow of Atlantic waters and the oceanic conveyor belt.

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Latest Pliocene through Holocene paleoceanography of the eastern Indian Ocean: benthic foraminiferal evidence

Multivariate analyses of latest Pliocene through Holocene benthic foraminifera from 61 samples from Deep-Sea Drilling Project (DSDP) Site 214, eastern Indian Ocean were carried out. The 46 highest ranked species were used in R-mode factor analysis which has enabled to the identification of three environmentally significant assemblages at Site 214. Assemblage 1 is characterized by Uvigerina hispido-costata, Osangularia culter, Gavelinopsis lobatulus, Cibicides wuellerstorfi and Karreriella baccata as principal species. This assemblage is inferred to reflect high-energy, well-oxygenated and probably low-organic carbon deep-sea environment at Site 214. Assemblage 2 is defined principally by Globocassidulina pacifica and U. proboscidea and is considered to indicate an organic carbon-rich environment which resulted from high surface productivity irrespective of dissolved oxygen content. Assemblage 3 is marked by Oridorsalis umbonatus, Textularia lythostrota, Hoeglundina elegans, Pyrgo murrhina, and Pullenia quinqueloba as principal species. This assemblage is inferred to indicate a low-organic carbon environment with high pore water oxygen concentration leading to better preservation of deep-sea sediments.

Late-glacial and Holocene paleoceanography and sedimentary environments in the St. Anna Trough, Eurasian Arctic Ocean margin

Based on stratigraphical analysis of twelve sediment cores from the Saint Anna Trough, we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the Holocene. Detailed analysis of benthic and planktic foraminiferal fauna, stable oxygen and carbon isotope analysis, lithostratigraphy and radiocarbon dates, are used to reconstruct the following evolution: After the deglaciation of the Saint Anna Trough >13,300 yr B.P. until 9500 yr B.P., the environment was mainly characterised by low biogenic production, carbonate dissolution and deposition of proximal to distal glaciomarine sediments. Intervals with high abundance of the benthic foraminifer Cassidulina teretis, may indicate influx of Atlantic Water at bottom. The transition into the present interglacial started at 9500 yr B.P. reflected by increased production of foraminifera and bivalves. After 8000 yr B.P. there was a marked drop in planktic δ18O followed by a rise in planktic foraminifera and subsequently an increase of C. teretis. These paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in Nordic seas. The early Holocene warming of the Saint Anna Trough were delayed by ca. 2000 years relative to the northeast Nordic seas. Early Holocene sedimentation rates were relatively high (>100 cm/1000 yr), declining drastically after 8000 yr B.P. (<50 cm/1000 yr). This was presumably caused by reduction in winnowing and/or riverine input.

Latest Quaternary and Holocene paleoceanography of the eastern Baffin Island continental shelf, Canada: benthic foraminiferal evidence

Foraminiferal zones, radiocarbon ages on shells, and corrected ages on pretreated organic sediment from four cores from the eastern Baffin Island continental shelf suggest a three-stage deglacial to postglacial history (Late Wisconsin to Holocene). The earliest sediments in the cores contain foraminiferal species (Elphidium excavatum, Cassidulina reniforme, Islandiella helenae) indicative of distal glaciomarine environments that lasted at least several thousand years. An oceanographic change about 8500 years ago is indicated by a Melonis zaandamae zone in northern and central shelf cores collected from 200–800 m water depth. The presence of M. zaandamae in the north and its absence in the south suggest warmer and more saline postglacial water in northern Baffin Bay, whose influence became diluted with cooler coastal meltwater as the current flowed south along the Baffin Island Shelf. Sediments after 6000 years ago on the northern and central shelf are dominated by agglutinated foraminifera, suggesting dissolution of calcareous species. This dissolution event, which affected deeper water cores sooner than cores from the shelf, may be related to the influx of cold, CO2-rich water from the Arctic Ocean during the mid-Holocene. Thus, postglacial oceanographic changes in Baffin Bay appear first in deep northern waters; the lag time in the response to these changes in the shallower water on the shelf and to the south may have been as long as several thousand years.

Upper Holocene Paleoceanography of Inner Miramichi Bay

Changes in sediment texture and in foraminiferal and molluscan assemblages observed in three vibracores collected in Miramichi Inner Boy reflect the development of a barrier island system across the mouth of the Bayt and the opening and closing of channels between the islands. The barrier island system apparently developed initially between 4400 and 3600 C14 years B.P. Opening and infilling of Buckleberry Gulley during the past 1300 years is indicated by changes in the proportions of estuarine and open bay assemblages of benthonic foraminifera. Mollusc and foraminifera data do not always suggest the same paleoenvironmental conditions at any given place and time, but they are in good agreement with respect to the direction of paleoenvironmental trends.