# North Atlantic Deglacial Isotope Data and Reconstructions of Salinity and SST #----------------------------------------------------------------------- # World Data Center for Paleoclimatology, Boulder # and # NOAA Paleoclimatology Program #----------------------------------------------------------------------- # NOTE: Please cite original publication, online resource and date accessed when using these data, # If there is no publication information, please cite investigator, title, online resource and date accessed. # # Online_Resource: http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:::::P1_STUDY_ID: # Online_Resource: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/thornalley2011/thornalley2011-17-5p-benth.txt # # Archive: Paleoceanography #-------------------- # Contribution_Date # Date: 2014-05-21 #-------------------- # Title # Study_Name: North Atlantic Deglacial Isotope Data and Reconstructions of Salinity and SST #-------------------- # Investigators # Investigators: Thornalley, D.J.R.; McCave, I.N.; Elderfield, H. #-------------------- # Description_and_Notes # Description: # #-------------------- # Publication # Authors: Thornalley, D.J.R., H. Elderfield, and I.N. McCave # Published_Date_or_Year: 2011 # Published_Title: Reconstructing North Atlantic deglacial surface hydrography and its link to the Atlantic overturning circulation # Journal_Name: Global and Planetary Change # Volume: 79 # Issue: # Pages: 163-175 # DOI: 10.1016/j.gloplacha.2010.06.003 # Abstract: Paired Mg/Ca-d18O measurements on multiple species of planktic foraminifera are combined with published benthic isotope records from south of Iceland in order to assess the role North Atlantic freshwater input played in determining the evolution of hydrography and climate during the last deglaciation. We demonstrate that Globigerina bulloides and Globorotalia inflata are restricted to intervals when warm Atlantic waters reached the area south of Iceland, and therefore Mg/Ca-d18O data from these species monitor changes in the temperature and seawater d18O signature of the northward inflow of Atlantic water to the area. In contrast, Neogloboquadrina pachyderma (sinistral) calcifies within local subpolar/polar waters and new Mg/Ca-d18O analyses on this species document changes in this water mass. We observe two major surface ocean events during Heinrich Stadial 1 (~ 17-14.7 ka): an early freshening of the Atlantic Inflow (~ 17-16 ka), and a later interval (16-14.7 ka) of local surface freshening, sea-ice formation and brine rejection that was associated with a further reduction in deep ocean ventilation. Centennial-scale cold intervals during the Bølling–Allerød (BA, 14.7-12.9 ka) were likely triggered by the rerouting of North American continental run-off during ice-sheet retreat. However, the relative effects of these freshwater events on deep ventilation and climate south of Iceland appear to have been modulated by the background climate deterioration. Two freshwater events occurred during the Younger Dryas cold interval (YD, 12.9-11.7 ka), both accompanied by a reduction in deep ventilation south of Iceland: an early YD freshening of the Atlantic Inflow and local subpolar/polar waters, and a late YD ice-rafted detritus event that was possibly related to brine formation south of Iceland. Based on our reconstructions, the strengthening of the Atlantic Meridional Overturning Circulation at the onset of BA and Holocene may have been promoted by the subsurface warming of subpolar/polar water, brine formation that drew warm saline Atlantic water northwards, and the high background salinity of the Atlantic Inflow. # #-------------------- # Publication # Authors: Thornalley, D.J.R., I.N. McCave, and H. Elderfield # Published_Date_or_Year: 2010 # Published_Title: Freshwater input and abrupt deglacial climate change in the North Atlantic # Journal_Name: Paleoceanography # Volume: 25 # Issue: # Report Number: PA1201 # DOI: 10.1029/2009PA001772 # Abstract: Greenland ice core records indicate that the last deglaciation (~7–21 ka) was punctuated by numerous abrupt climate reversals involving temperature changes of up to 5°C–10°C within decades. However, the cause behind many of these events is uncertain. A likely candidate may have been the input of deglacial meltwater, from the Laurentide ice sheet (LIS), to the high-latitude North Atlantic, which disrupted ocean circulation and triggered cooling. Yet the direct evidence of meltwater input for many of these events has so far remained undetected. In this study, we use the geochemistry (paired Mg/Ca-d18O) of planktonic foraminifera from a sediment core south of Iceland to reconstruct the input of freshwater to the northern North Atlantic during abrupt deglacial climate change. Our record can be placed on the same timescale as ice cores and therefore provides a direct comparison between the timing of freshwater input and climate variability. Meltwater events coincide with the onset of numerous cold intervals, including the Older Dryas (14.0 ka), two events during the Allerød (at ~13.1 and 13.6 ka), the Younger Dryas (12.9 ka), and the 8.2 ka event, supporting a causal link between these abrupt climate changes and meltwater input. During the Bølling-Allerød warm interval, we find that periods of warming are associated with an increased meltwater flux to the northern North Atlantic, which in turn induces abrupt cooling, a cessation in meltwater input, and eventual climate recovery. This implies that feedback between climate and meltwater input produced a highly variable climate. A comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the LIS causing rerouting of LIS meltwater between southern and eastern drainage outlets, as proposed by Clark et al. (2001). #-------------------- # Publication # Authors: Thornalley, D.J.R., H. Elderfield, and I.N. McCave # Published_Date_or_Year: 2010 # Published_Title: Intermediate and Deep Water Paleoceanography of the Northern North Atlantic Over the Past 21,000 years # Journal_Name: Paleoceanography # Volume: 25 # Issue: 1 # Report Number: PA1211 # DOI: 10.1029/2009PA001833 # Abstract: Benthic foraminiferal stable isotope records from four high-resolution sediment cores, forming a depth transect between 1237 m and 2303 m on the South Iceland Rise, have been used to reconstruct intermediate and deep water paleoceanographic changes in the northern North Atlantic during the last 21 ka (spanning Termination I and the Holocene). Typically, a sampling resolution of ~100 years is attained. Deglacial core chronologies are accurately tied to North Greenland Ice Core Project (NGRIP) ice core records through the correlation of tephra layers and changes in the percent abundance of Neogloboquadrina pachyderma (sinistral) with transitions in NGRIP. The evolution from the glacial mode of circulation to the present regime is punctuated by two periods with low benthic d13C and d18O values, which do not lie on glacial or Holocene water mass mixing lines. These periods correlate with the late Younger Dryas/Early Holocene (11.5-12.2 ka) and Heinrich Stadial 1 (14.7-16.8 ka) during which time freshwater input and sea-ice formation led to brine rejection both locally and as an overflow exported from the Nordic seas into the northern North Atlantic, as earlier reported by Meland et al. (2008). The export of brine with low d13C values from the Nordic seas complicates traditional interpretations of low d13C values during the deglaciation as incursions of southern sourced water, although the spatial extent of this brine is uncertain. The records also reveal that the onset of the Younger Dryas was accompanied by an abrupt and transient (~200-300 year duration) decrease in the ventilation of the northern North Atlantic. During the Holocene, Iceland-Scotland Overflow Water only reached its modern flow strength and/or depth over the South Iceland Rise by 7–8 ka, in parallel with surface ocean reorganizations and a cessation in deglacial meltwater input to the North Atlantic. #-------------------- # Publication # Authors: Thornalley, D.J.R., H. Elderfield, and I.N. McCave # Published_Date_or_Year: 2009 # Published_Title: Holocene oscillations in temperature and salinity of the subpolar North Atlantic # Journal_Name: Nature # Volume: 457 # Issue: 5 # Pages: 711-714 # DOI: 10.1038/nature07717 # Abstract: The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch (~11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity (~3.5°C and ~1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes, although the inflow can compensate on decadal timescales by becoming more saline. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change. #--------------------- # Funding_Agency # Funding_Agency_Name: # Grant: #--------------------- # Site_Information # Site_Name: RAPiD-17-5P # Location: North Atlantic Ocean # Country: # Northernmost_Latitude: 61.481667 # Southernmost_Latitude: 61.481667 # Easternmost_Longitude: -19.536 # Westernmost_Longitude: -19.536 # Elevation: -2303 #------------------ # Data_Collection # Collection_Name: RAPiD-17-5P Benthics Th11 # Earliest_Year: 21726 # Most_Recent_Year: 3943 # Time_Unit: calyr BP # Core_Length: # Notes: C. wuell. originally presented in Thornalley, Elderfield & McCave, 2010, Paleoceanography, 2009PA001833. # Stable isotope values relative to VPDB standard, run in Godwin Laboratory, Univ. of Cambridge # # "Ice-volume corrected" for whole ocean changes using Fairbanks (1989) sea-level curve, assuming a LGM to late Holocene shift of 1 ‰ # #------------------ # Chronology: # # #------------------ # Variables # # Data line variables format: one variable per line, shortname- 9 components: what, material, error, units, seasonality, archive, detail, method, C or N for Character or Numeric data) # Data line format: tab-delimited text, variable short name as header ## depth_cm depth,,,cm,,,,,N ## age_calkaBP2000 age,,,calendar kyr before 2000AD,,,,,N ## d18Oc.wuell delta 18O,Cibicidoides wuellerstorfi,,per mil VPDB,,paleoceanography,,,N ## d18Oc.wuell-ivc delta 18O,Cibicidoides wuellerstorfi ice-volume corrected,,per mil VPDB,,paleoceanography,,,N ## d13Cc.wuell delta 13C,Cibicidoides wuellerstorfi,,per mil VPDB,,paleoceanography,,,N #----------------- # Data: # Missing Value: NaN depth_cm age_calkaBP2000 d18Oc.wuell d18Oc.wuell-ivc d13Cc.wuell 328.5 3.993 2.75 2.67 1.26 592.5 7.462 2.85 2.70 1.25 648.5 8.198 3.02 2.87 1.25 656.5 8.304 2.90 2.75 1.20 664.5 8.409 2.90 2.75 1.25 726.5 9.224 2.94 2.74 0.94 734.5 9.329 3.00 2.79 0.92 750.5 9.539 3.03 2.81 0.64 766.5 9.654 2.99 2.75 0.60 806.5 9.943 3.06 2.80 0.81 880.5 10.698 3.19 2.88 0.68 900.5 11.089 3.04 2.71 0.87 912.5 11.323 3.17 2.79 0.95 918.5 11.440 3.13 2.73 0.90 928.5 11.746 3.12 2.68 0.49 930.5 11.823 3.18 2.74 0.49 948.5 11.977 3.89 3.44 0.80 950.5 12.054 3.80 3.35 0.73 952.5 12.131 3.95 3.49 0.96 956.5 12.760 3.69 3.19 0.88 958.5 12.893 3.69 3.19 0.97 960.5 13.027 3.64 3.13 0.72 962.5 13.160 3.81 3.29 0.93 964.5 13.380 3.80 3.27 0.71 966.5 13.600 3.92 3.37 0.91 967.5 13.710 3.72 3.16 0.94 968.5 13.820 3.72 3.15 0.96 969.5 13.930 3.75 3.14 0.80 970.5 14.040 3.78 3.13 0.94 971.5 14.150 3.74 3.05 0.85 972.5 14.260 3.70 2.98 0.91 973.5 14.370 3.70 2.97 0.70 974.5 14.480 3.74 3.00 0.64 975.5 14.590 3.77 3.02 0.51 976.5 14.700 3.70 2.94 0.32 977.5 14.839 3.76 3.00 0.45 978.5 14.978 3.63 2.86 0.18 979.5 15.117 3.76 2.99 0.22 980.5 15.256 3.69 2.92 0.14 981.5 15.394 3.74 2.96 0.11 982.5 15.533 3.73 2.95 -0.14 983.5 15.672 3.83 3.04 0.19 985.5 15.950 3.61 2.82 0.53 986.5 16.089 4.22 3.42 0.31 987.5 16.228 4.56 3.76 0.62 988.5 16.367 4.25 3.45 0.58 989.5 16.506 4.34 3.54 0.64 990.5 16.644 4.50 3.69 0.53 991.5 16.783 4.63 3.81 0.57 992.5 16.922 4.57 3.75 0.68 993.5 17.061 4.57 3.74 0.67 994.5 17.200 4.64 3.81 0.69 1004.5 17.992 4.62 3.77 0.74 1005.5 18.072 4.51 3.66 0.59 1006.5 18.151 4.56 3.70 0.63 1007.5 18.230 4.56 3.71 0.69 1008.5 18.309 4.55 3.69 0.62 1009.5 18.388 4.65 3.79 0.38 1010.5 18.468 4.58 3.72 0.63 1011.5 18.547 4.69 3.82 0.70 1012.5 18.626 4.47 3.60 0.67 1013.5 18.705 4.60 3.72 0.64 1020.5 19.260 4.47 3.54 0.60 1031.5 20.132 4.71 3.76 0.72 1032.5 20.211 4.28 3.32 0.45 1033.5 20.290 4.61 3.66 0.59 1034.5 20.369 4.65 3.69 0.67 1035.5 20.448 4.62 3.65 0.65 1036.5 20.528 4.60 3.63 0.57 1037.5 20.607 4.66 3.69 0.83 1040.5 20.845 4.28 3.31 0.60 1044.5 21.162 4.54 3.56 0.63 1045.5 21.241 4.62 3.63 0.70 1046.5 21.320 4.46 3.48 0.58 1047.5 21.399 4.53 3.54 0.54 1048.5 21.478 4.30 3.31 0.46 1049.5 21.558 4.52 NaN 0.56 1050.5 21.637 4.54 NaN 0.73 1051.5 21.766 4.49 NaN 0.60