# 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/thornalley2011-12-1k-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-12-1K # Location: North Atlantic Ocean # Country: # Northernmost_Latitude: 62.0905 # Southernmost_Latitude: 62.0905 # Easternmost_Longitude: -17.819667 # Westernmost_Longitude: -17.819667 # Elevation: -1938 #------------------ # Data_Collection # Collection_Name: RAPiD-12-1K benthics Th11 # Earliest_Year: 11693 # Most_Recent_Year: 0 # Time_Unit: calyr BP # Core_Length: # Notes: Please cite Thornalley, Elderfield & McCave, 2010, Paleoceanography, 2009PA001833. # Stable isotope values relative to VPDB standard, run in Godwin Laboratory, Univ. of Cambridge; vital effect of -0.24 applied to Melonis d18O data # # "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_top depth bottom of sample interval,,,cm,,paleoceanography,,,N ## depth_bot depth top of sample interval,,,cm,,paleoceanography,,,N ## depth_cm depth,,,cm,,,,,N ## age_calkaBP age,,,calendar kyr before 1950AD,,,,,N ## numshells number of shells,,, ,,paleoceanography,,,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 ## d18Om.barle-.24 delta 18O,Melonis barleanuum,,per mil VPDB,,paleoceanography,vital effect of -0.24 applied,,N ## d18Om.barle-ivc delta 18O,Melonis barleanuum ice-volume corrected,,per mil VPDB,,paleoceanography,,,N ## notes notes,,, ,,,,,C #----------------- # Data: # Missing Value: NaN depth_top depth_bot depth_cm age_calkaBP d18Oc.wuell d18Oc.wuell-ivc d13Cc.wuell notes 0 1 0.5 0.000 15 2.82 2.82 1.24 NaN NaN 8 9 8.5 0.250 18 2.79 2.78 1.38 NaN NaN 16 17 16.5 0.500 20 2.80 2.79 1.40 NaN NaN 24 25 24.5 0.771 10 2.82 2.80 1.36 NaN NaN number of shells: >10 32 33 32.5 1.064 10 2.80 2.78 1.39 NaN NaN number of shells: >10 40 41 40.5 1.357 10 2.79 2.76 1.42 NaN NaN number of shells: >10 48 49 48.5 1.650 18 2.82 2.79 1.36 NaN NaN 56 57 56.5 1.917 12 2.82 2.78 1.41 NaN NaN 64 65 64.5 2.158 23 2.82 2.78 1.34 NaN NaN 72 73 72.5 2.399 17 2.74 2.70 1.34 NaN NaN 80 81 80.5 2.640 17 2.81 2.76 1.39 NaN NaN 88 89 88.5 2.881 15 2.79 2.74 1.42 NaN NaN 96 97 96.5 3.347 21 2.78 2.71 1.46 NaN NaN 104 105 104.5 3.814 19 2.82 2.74 1.42 NaN NaN 112 113 112.5 4.281 21 2.95 2.86 1.38 NaN NaN 120 121 120.5 4.802 15 2.95 2.85 1.36 NaN NaN 128 129 128.5 5.378 22 2.86 2.75 1.39 NaN NaN 136 137 136.5 5.953 15 2.83 2.71 1.41 NaN NaN 144 145 144.5 6.529 19 2.96 2.83 1.15 NaN NaN 152 153 152.5 6.909 21 3.03 2.90 1.19 NaN NaN 160 161 160.5 7.290 22 3.01 2.87 1.14 NaN NaN 168 169 168.5 7.670 18 2.89 2.74 1.26 NaN NaN 176 177 176.5 8.051 7 2.96 2.81 1.30 NaN NaN 184 185 184.5 8.133 1 2.95 2.80 1.44 NaN NaN 192 193 192.5 8.216 2 3.10 2.95 0.82 NaN NaN 200 201 200.5 8.298 3 2.99 2.84 1.31 NaN NaN 208 209 208.5 8.380 2 2.93 2.78 1.01 NaN NaN 216 217 216.5 8.463 1 2.87 2.72 1.24 NaN NaN 224 225 224.5 8.592 1 2.91 2.74 1.19 NaN NaN 232 233 232.5 8.722 3 3.10 2.93 0.57 NaN NaN 240 241 240.5 8.852 8 3.28 3.10 0.56 NaN NaN 248 249 248.5 8.982 21 3.44 3.26 0.78 NaN NaN 256 257 256.5 9.112 10 2.98 2.78 1.05 NaN NaN 264 265 264.5 9.241 11 3.31 3.11 0.83 NaN NaN 272 273 272.5 9.371 9 3.24 3.03 0.76 NaN NaN 280 281 280.5 9.501 10 3.04 2.82 0.93 NaN NaN 288 289 288.5 9.631 11 3.06 2.83 0.61 NaN NaN 312 313 312.5 9.878 3 3.15 2.90 0.67 NaN NaN 320 321 320.5 9.913 2 3.42 3.17 0.98 NaN NaN 328 329 328.5 9.948 1 3.11 2.85 1.05 NaN NaN 347 348 347.5 10.031 NaN NaN NaN NaN 3.10 2.84 359 360 359.5 10.084 2 2.81 2.54 1.19 NaN NaN 376 377 376.5 10.158 1 2.77 2.50 0.87 NaN NaN 380 381 380.5 10.175 NaN NaN NaN NaN 2.93 2.66 412 413 412.5 10.280 NaN NaN NaN NaN 3.02 2.74 444 445 444.5 10.373 1 3.12 2.84 0.43 NaN NaN 460 461 460.5 10.483 NaN NaN NaN NaN 3.01 2.72 464 465 464.5 10.516 NaN NaN NaN NaN 3.03 2.74 468 469 468.5 10.549 NaN NaN NaN NaN 2.97 2.67 472 473 472.5 10.582 NaN NaN NaN NaN 2.98 2.68 492 493 492.5 10.729 NaN NaN NaN NaN 2.96 2.65 508 509 508.5 10.838 NaN NaN NaN NaN 3.02 2.71 540 541 540.5 11.055 NaN NaN NaN NaN 2.95 2.62 572 573 572.5 11.273 NaN NaN NaN NaN 2.99 2.62 584 585 584.5 11.355 NaN NaN NaN NaN 2.71 2.33 588 589 588.5 11.391 NaN NaN NaN NaN 2.89 2.50 608 609 608.5 11.586 1 3.22 2.79 1.11 NaN NaN 611 612 611.5 11.615 6 2.90 2.47 0.56 NaN NaN 619 620 619.5 11.693 1 2.95 2.52 0.66 NaN NaN