Oxygen isotope compositions of sinistral Neogloboquadrina pachyderma tests in surface sediments: North Atlantic Ocean (original) (raw)
Related papers
We determined oxygen isotope ratios (δ 18 O) of the mixed layerdwelling planktonic foraminifer Globigerina bulloides and relative abundance of Neogloboquadrina pachyderma (sinistral) for the last glacial-interglacial cycle, including marine isotope Stage (MIS) 6 from Integrated Ocean Drilling Program Site U1313. The δ 18 O data in G. bulloides allowed us to construct an age model. Changes in relative abundance of N. pachyderma (s) were compared to the δ 18 O of G. bulloides. We also performed a detailed quantitative study of four planktonic foraminiferal species to assess surface to near-surface oceanographic changes for the period between MIS 5e and 6 (120-180 ka), including the penultimate glacial termination (TII). Analyses of the relative abundances of four planktonic foraminiferal species lead us to reconstruct the variability in the upper water masses of the North Atlantic at this subtropical site. We found clear indications of freshwater inputs, including a Heinrich iceberg-rafting event (H11), which provided a mechanism for freshening the sea surface and perturbing climate conditions.
2000
We present measurements of the maximum diameter of the planktonic foraminifer Neogloboquadrina pachyderma sin. from six sediment cores (Ocean Drilling Program sites 643, 644, 907, 909, 985 and 987) from the Norwegian-Greenland Sea. Our data show a distinct net increase in mean shell size of N. pachyderma sin. at all sites during the last 1.3 Ma, with largest shell sizes reached after 0.4 Ma. External factors such as glacial-interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of N. pachyderma sin. We consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of N. pachyderma sin. to the cold water environment after 1.1-1.0 Ma. Probably, the Mid Pleistocene climate shift and the associated change of amplitude and frequency of glacial-interglacial fluctuations have triggered the evolution of this planktonic foraminifer. Oxygen and carbon stable isotope analyses of different shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis. For paleoceanographic reconstructions, the evolutionary adaptation of Neogloboquadrina pachyderma sin. to the cold water habitat has significant implications. Carbonate sedimentation in highest latitudes is highly dependent on the presence of this species. In the Norwegian-Greenland Sea, carbonate-poor intervals before 1.1 Ma are, therefore, not necessarily related to severe glacial conditions. They are probably attributed to the absence of this not yet polar-adapted species. Further, transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could, therefore, contain a large range of errors if they were applied to samples older than 1.1-1.0 Myrs.
Quaternary Science Reviews, 2004
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 d 13 C and d 18 O-values are size and weight dependent. However, whereas the Npl 18 O data from the NW Atlantic indicate near-equilibrium conditions with ambient waters and a positive relationship between shell weight and 18 O-content, assemblages from box-cored sediments of the Chukchi Sea (western Arctic) are depleted by B2% with respect to equilibrium values with modern conditions, and depict a negative relationship between shell weight and its d 18 O-value (À0.1570.03%/mg 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. d 18 O 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 d 18 O-values in both Npl and Npd together with larger d 18 O-gradients between the different shell sizes at ca 9-7 ka BP suggest B3 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. r
Palaeogeography, Palaeoclimatology, Palaeoecology, 2000
We present measurements of the maximum diameter of the planktonic foraminifer Neogloboquadrina pachyderma sin. from six sediment cores (Ocean Drilling Program sites 643, 644, 907, 909, 985 and 987) from the Norwegian-Greenland Sea. Our data show a distinct net increase in mean shell size of N. pachyderma sin. at all sites during the last 1.3 Ma, with largest shell sizes reached after 0.4 Ma. External factors such as glacial-interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of N. pachyderma sin. We consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of N. pachyderma sin. to the cold water environment after 1.1-1.0 Ma. Probably, the Mid Pleistocene climate shift and the associated change of amplitude and frequency of glacial-interglacial fluctuations have triggered the evolution of this planktonic foraminifer. Oxygen and carbon stable isotope analyses of different shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis. For paleoceanographic reconstructions, the evolutionary adaptation of Neogloboquadrina pachyderma sin. to the cold water habitat has significant implications. Carbonate sedimentation in highest latitudes is highly dependent on the presence of this species. In the Norwegian-Greenland Sea, carbonate-poor intervals before 1.1 Ma are, therefore, not necessarily related to severe glacial conditions. They are probably attributed to the absence of this not yet polar-adapted species. Further, transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could, therefore, contain a large range of errors if they were applied to samples older than 1.1-1.0 Myrs.
Quaternary Science Reviews, 2002
We review the various methods which have been applied to estimate the change of seawater d 18 O (dw) between the Last Glacial Maximum (LGM) and the Holocene. The most accurate constraints on these estimates are provided by the measurement of pore waters d 18 O and by high resolution records of benthic foraminifer d 18 O in the high latitude oceans of both hemispheres. They show that the d 18 O of seawater in the deep ocean during the LGM was 1.0570.20% heavier than today, with significant regional variations. Constraints resulting from ice sheet models are less accurate, because both the volume and isotopic composition of each ice sheet are still poorly known. The amplitude of the benthic d 18 O change between the LGM and the Holocene, together with the d 18 O and d 13 C values of the benthic foraminifera genus Cibicides during the LGM, show that the Southern Ocean deep waters were extremely cold, close to the freezing point. During this time, deep waters of the South Atlantic and the Pacific oceans were at least 1.31C warmer than those of the Southern Ocean. Overall, the glacial deep ocean, below 2500 m, was characterized by extremely cold temperatures, everywhere lower than 01C. d 18 O values of benthic foraminifer from the North Atlantic are highly variable. This variability suggests that deep Atlantic waters were not homogeneous, probably because they resulted from the sinking of different surface water masses at various locations during winter. The deep waters in the North Atlantic were at most 21C warmer than in Southern Ocean. Alternatively, they could have been nearer the freezing point with a d 18 O value lighter than the mean ocean water. Brine formation during winter would preserve such light d 18 O values of the northern North Atlantic surface water.
IOP Conference Series: Earth and Environmental Science, 2011
Since the reassessment of oxygen isotope paleotemperatures by N. Shackleton in the late 60s, most papers using isotopic records from planktic or benthic foraminifers imply a direct relationship between oxygen isotopes in seawater and the ice/ocean volume, thus some linkage with salinity, sea level, etc. Such assumptions are also made when incorporating "isotopic modules" in coupled models. Here, we will further examine the linkages between salinity and oxygen isotope ratios of seawater recorded by foraminifers, and their potential temporal and spatial variability, especially in the northern North Atlantic and the Arctic oceans. If temporal and spatial changes in the isotopic composition of precipitations and ice meltwaters tune the isotopic properties of the fresh water end-member that dilutes the ocean, rates of sea-ice formation and evaporation at the ocean surface play a further role on the salt and oxygen isotope contents of water masses. Thus, the oxygen 18-salinity relationship carries a specific isotopic signature for any given water mass. At the ocean scale, residence time and mixing of these water masses, as well as the time dependent-achievement of proxy-tracer equilibrium, will also result in variable recordings of mass transfers into the hydrosphere, notable between ice-sheets and ocean. Since these records in water mass may vary in both amplitude and time, direct correlations of isotopic records will potentially be misleading. Implications of such issues on the interpretation of oxygen isotope records from the sub-arctic seas will be discussed, as well as the inherent flaws of such records due to sedimentological and or ecological parameters.
The Holocene, 2014
Holocene sea surface temperatures in the eastern Fram Strait are reconstructed based on Mg/Ca ratios measured on the planktic foraminifer Neogloboquadrina pachyderma (sin). The reconstructed sub sea surface temperatures (sSSTMg/Ca) fluctuate markedly during the earliest Holocene at ~11.7-10.5 ka BP. This probably is in response to the varying presence of sea ice and deglacial melt water. Between ~10.5-7.9 ka BP the sSSTMg/Ca values are relatively high (~4°C) and more stable reflecting high insolation and intensified poleward advection of Atlantic water. After 7.9 ka BP the sSSTMg/Ca decline to an average of ~3°C throughout the mid-Holocene. These changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating Arctic Water. The sSSTMg/Ca increase and vary between 2.1-5.8°C from ~2.7 ka BP to the present. This warming is in contrast to declining late Holocene insolation and may instead be explained by factors including increased advection of oceanic heat to the Arctic region possibly insulated beneath a widening freshwater layer in the northern North Atlantic in conjunction with a shift in calcification season and/or depth habitat of N. pachyderma (sin).
Quaternary Science Reviews, 2002
We review the various methods which have been applied to estimate the change of seawater d 18 O (dw) between the Last Glacial Maximum (LGM) and the Holocene. The most accurate constraints on these estimates are provided by the measurement of pore waters d 18 O and by high resolution records of benthic foraminifer d 18 O in the high latitude oceans of both hemispheres. They show that the d 18 O of seawater in the deep ocean during the LGM was 1.0570.20% heavier than today, with significant regional variations. Constraints resulting from ice sheet models are less accurate, because both the volume and isotopic composition of each ice sheet are still poorly known. The amplitude of the benthic d 18 O change between the LGM and the Holocene, together with the d 18 O and d 13 C values of the benthic foraminifera genus Cibicides during the LGM, show that the Southern Ocean deep waters were extremely cold, close to the freezing point. During this time, deep waters of the South Atlantic and the Pacific oceans were at least 1.31C warmer than those of the Southern Ocean. Overall, the glacial deep ocean, below 2500 m, was characterized by extremely cold temperatures, everywhere lower than 01C. d 18 O values of benthic foraminifer from the North Atlantic are highly variable. This variability suggests that deep Atlantic waters were not homogeneous, probably because they resulted from the sinking of different surface water masses at various locations during winter. The deep waters in the North Atlantic were at most 21C warmer than in Southern Ocean. Alternatively, they could have been nearer the freezing point with a d 18 O value lighter than the mean ocean water. Brine formation during winter would preserve such light d 18 O values of the northern North Atlantic surface water.
Quaternary Science Reviews, 2014
Estimates of the change in surface seawater d 18 O (d 18 O sw) between the Last Glacial Maximum (LGM) and Late Holocene (LH) are derived from homogenous data sets with rigorous age control, namely MARGO sea surface temperature (SST) estimates and oxygen isotopic ratios (d 18 O) of planktonic foraminifers. Propagation of uncertainties associated with each proxy allows the identification of robust patterns of change in d 18 O sw. Examination of these patterns on a regional scale highlights which changes in surface currents and hydrological cycle are consistent with both planktonic isotopic data and reconstructed SST. Positive local annual mean LGM-LH d 18 O sw anomalies characterize the glacial tropical Indian Ocean, portions of the western and eastern margins of the North Pacific, the Iberian margin and the tropical North Atlantic, as well as the South African margin. Although reduced precipitation during the LGM with respect to the LH may have contributed to some extent to these local enrichments in surface seawater 18 O, the largest positive anomalies appear to be related to changes in ocean circulation. Large local negative annual mean LGM-LH d 18 O sw anomalies are found in the South Pacific and North Atlantic, reflecting the equatorward migration of surface temperature fronts during the LGM with respect to the LH. In the northern North Atlantic, a region characterized by large discrepancies between SST estimates based on different proxies, only SST estimates based on planktonic foraminifer counts yield annual mean LGM-LH d 18 O sw anomalies consistent with a southward shift of the polar front at the LGM relative to the LH.
A Late Glacial–Early Holocene multiproxy record from the eastern Fram Strait, Polar North Atlantic
2014
The paleoceanographic development of the eastern Fram Strait during the transition from the cold Late Glacial and into the warm early Holocene was elucidated via a multiproxy study of a marine sediment record retrieved at the western Svalbard slope. The multiproxy study includes analyses of planktic foraminiferal fauna, bulk sediment grain size and CaCO 3 content in addition to Mg/Ca ratios and stable isotopes (δ 13 C and δ 18 O) measured on the planktic foraminifer Neogloboquadrina pachyderma. Furthermore paleo subsurface water temperatures were reconstructed via Mg/Ca ratios (sSST Mg/Ca) and transfer functions (sSST Transfer) enabling comparison between the two proxies within a single record. The age model was constrained by four accelerator mass spectrometry (AMS) 14 C dates. From 14,000 to 10,300 cal yr B.P. N. pachyderma dominated the planktic fauna and cold polar sea surface conditions existed. The period was characterized by extensive sea ice cover, iceberg transport and low sub sea surface temperatures (sSST Transfer ~2.1°C; sSST Mg/Ca ~3.5°C) resulting in restricted primary production. Atlantic Water inflow was reduced compared to the present-day and likely existed as a subsurface current. At ca. 10,300 cal yr B.P. Atlantic Water inflow increased and the Arctic Front retreated north-westward resulting in increased primary productivity, higher foraminiferal fluxes and a reduction in sea ice cover and iceberg transport. The fauna rapidly became dominated by the subpolar planktic foraminifer Turborotalita quinqueloba and summer sSST Transfer increased by ~3.5°C. Concurrently, the sSST Mg/Ca recorded by N. pachyderma rose only ~0.5°C. From ca. 10,300 to 8,600 cal yr B.P. the average sSST Mg/Ca and sSST Transfer were ~4.0°C and ~5.5°C, respectively. The relatively modest change in sSST Mg/Ca compared to sSST Transfer can probably be tied to a change of the main habitat depth and/or shift in the calcification season for N. pachyderma during this period.