Heinrich summers
34
Citation
110
Reference
10
Related Paper
Citation Trend
Keywords:
Meltwater
Iceberg
Westerlies
Paleoclimatology
We introduce explicit icebergs from a dynamic and thermodynamic iceberg model into an intermediate complexity climate model, which includes the coupled atmosphere‐ocean system. This modeling approach allows iceberg meltwater to be injected into the ocean on the basis of thermodynamical considerations along the iceberg trajectories. Icebergs are seeded from known ice sheets in both hemispheres. Adding icebergs to the present‐day climate model has a minimal impact, but during the Last Glacial Maximum (LGM), Atlantic overturning strength is reduced by a third, while producing a model state that is consistent with a steady state climate. We test the sensitivity of the model at the LGM to additional Heinrich event‐scale fluxes of icebergs from three possible sources: Hudson Strait, the Gulf of Saint Lawrence, and the Norwegian Channel Ice Stream (NCIS). The sensitivity of the ocean is similar for all locations, with differences dominated by the length of the iceberg meltwater pathways to the main ocean convection region. The NCIS events result in more variability and a distinctly different, more northerly, salinity anomaly. We compare these results to a more typical modeling approach, whereby meltwater is injected directly into the ocean at the iceberg source locations, and find that these floods overestimate the oceanic response compared to the iceberg events. Our results suggest that 0.3–0.4 Sv of additional freshwater flux, either as icebergs or freshwater, is required to shut down the North Atlantic meridional overturning, a larger freshwater flux than sometimes suggested because of the localized nature of the release of the freshwater.
Iceberg
Meltwater
Last Glacial Maximum
Cite
Citations (79)
Abstract High resolution seafloor mapping shows extraordinary evidence that massive (>300 m thick) icebergs once drifted >5,000 km south along the eastern United States, with >700 iceberg scours now identified south of Cape Hatteras. Here we report on sediment cores collected from several buried scours that show multiple plow marks align with Heinrich Event 3 (H3), ~31,000 years ago. Numerical glacial iceberg simulations indicate that the transport of icebergs to these sites occurs during massive, but short-lived, periods of elevated meltwater discharge. Transport of icebergs to the subtropics, away from deep water formation sites, may explain why H3 was associated with only a modest increase in ice-rafting across the subpolar North Atlantic, and implies a complex relationship between freshwater forcing and climate change. Stratigraphy from subbottom data across the scour marks shows there are additional features that are both older and younger, and may align with other periods of elevated meltwater discharge.
Iceberg
Meltwater
Forcing (mathematics)
Seafloor Spreading
Cite
Citations (16)
Observations in South America based on paleoenvironmental data for the Last Glacial Maximum (LGM) that shows a generally lower temperatures and reduced precipitation of the region are compared to simulation results from the paleoclimate version of the National Center for Atmospheric Research coupled climate system model. Analyses of the LGM wind simulation for the tropical Atlantic show that the convergence zone does not extend all the way into South American continent during the Austral summer. This would have prevented moisture inflow into the adjacent continental area of equatorial northeastern Brazil. Interpretations of paleoclimate proxy records from this region are consistent with this scenario. In the subtropics, LGM westerlies were weaker and data show characteristics of more humid conditions. At higher latitudes model simulations suggest intensification of the westerlies which, in combination with colder sea surface temperatures would imply less moisture influx into the South American continent from the Atlantic sector. Low lake levels in high southern latitudes and general aridity would support the model findings.
Paleoclimatology
Westerlies
Last Glacial Maximum
Cite
Citations (39)
High resolution seafloor mapping shows extraordinary evidence that massive (>300m thick) icebergs once drifted >5,000km south along the eastern United States, with over 700 iceberg scours now identified south of Cape Hatteras. Sediment cores collected from several buried scours show multiple plow marks are ~31,000 years old and align with Heinrich Event 3 (H3). An accompanying set of numerical glacial iceberg simulations performed with an eddy permitting ocean model show that the transport of icebergs to these sites only occurs during massive, but short-lived, periods of elevated meltwater discharge. As H3 was associated with only a modest increase in ice-rafting across the subpolar North Atlantic, we propose that meltwater and icebergs were repeatedly routed to the subtropics during this event. Stratigraphy from subbottom data across the scour marks shows there are additional features that are both older and younger, and may align with other periods of elevated meltwater discharge. Finally, the subtropical iceberg-meltwater pathway identified supports a complex relationship between freshwater forcing and climate change given meltwater may initially be routed far to the south of deep-water formation sites.
Iceberg
Meltwater
Cite
Citations (1)
Monthly Iceberg Meltwater Fluxes over the Southern Ocean (1972-2017) : Here is an update of the iceberg meltwater climatology initially provided by Merino et al (2016). This flux is still derived from NEMO's Lagrangian iceberg module developed by Marsh et al. (2015) and updated by Merino et al. (2016). It is run within a global ORCA025 ocean simulation running from 1958 to 2017, forced by the Drakkar Forcing Set (DFS-5.2; Dussin et al 2016). The 1958-1972 period is used to spin up the model, and the meltwater fluxes are provided over 1972-2017. The iceberg calving fluxes are constant, but their meltwater fluxes varies seasonally and interannually. Ice-shelf meltwater fluxes are reconstructed from glaciological observations (Merino et al. 2018), and here vary linearly from 1990 to 2010 (constant before and after). Known caveats: The ocean grid is the old "ORCA025" grid, which does not extend southward of 70°S, i.e. iceberg do not follow the southernmost ice shelf edges (e.g. Ronne ice shelf). References: Dussin, Raphael, Bernard Barnier, Laurent Brodeau, and Jean Marc Molines (2016). Drakkar Forcing Set DFS5. Marsh, R., Ivchenko, V. O., Skliris, N., Alderson, S., Bigg, G. R., Madec, G., and others (2015). NEMO-ICB (v1. 0): interactive icebergs in the NEMO ocean model globally configured at eddy-permitting resolution. Geoscientific Model Development, 8(5), 1547-1562. Merino, N., Le Sommer, J., Durand, G., Jourdain, N. C., Madec, G., Mathiot, P. and Tournadre, J. (2016). Antarctic icebergs melt over the Southern Ocean: Climatology and impact on sea ice. Ocean Modelling, 104, 99-110. Merino, N., Jourdain, N. C., Le Sommer, J., Goosse, H., Mathiot, P. and Durand, G. (2018). Impact of increasing antarctic glacial freshwater release on regional sea-ice cover in the Southern Ocean. Ocean Modelling, 121, 76-89.
Iceberg
Meltwater
Cite
Citations (8)
The distribution of sea ice meltwater and meteoric water in the eastern Canadian Arctic has been studied by oxygen isotope techniques. The distribution pattern of sea ice meltwater is presented. A comparison of the relative amounts of sea ice meltwater and meteoric water in the surface layer shows that more than 25% of all the samples with sea ice input contained more sea ice input than meteoric input. Sea ice meltwater/meteoric water ratios as high as 4.7 have been observed. The depth of sea ice meltwater penetration varies from 50 m in Baffin Bay to 140 m in Lancaster Sound. Calculated sea ice thicknesses range from 0.5 to 4.5 m with a mean of 1.5 m, in good agreement with ice core data. The significance of sea ice meltwater for chemical, physical, and biological oceanography is briefly discussed. The principles and limitations of using oxygen isotopes to detect brines are discussed in the Baffin Bay setting. The isotopic compositions of possible source waters for Baffin Bay bottom water are examined.
Meltwater
Fast ice
Melt pond
Cite
Citations (86)
An iceberg drift and decay model that computes the long‐term ice‐rafted debris (IRD) and iceberg meltwater flux over an entire ocean basin is presented. The model requires atmospheric and oceanic flow fields and has three main operations: iceberg drift, decay, and debris release. Using present atmospheric and oceanic flow fields in the North Atlantic, the model is able to reproduce modern iceberg drift paths and seasonal iceberg occurrences. Using the same flow fields, IRD and iceberg meltwater flux to the North Atlantic are computed. Core‐top data do not preserve an adequate record of present‐day IRD distribution on the ocean floor; thus modeled IRD results are compared with IRD results from marine isotopic stage 5e (the last interglacial), a period most similar to present interglacial conditions. Similarity between the modeled and observed IRD patterns confirms that present ocean surface conditions affecting iceberg drift and decay are similar to those of stage 5e. Detailed comparison reveals icebergs from stage 5e reaching as far east as 20°W, which is not reproduced by the model under existing oceanographic conditions. This discordance suggests that the 5e IRD data set includes deposits from times colder than today, either because of truly colder intervals in 5e or because of dating uncertainties in the data. Modeled meltwater flux to the North Atlantic exhibits large seasonal and spatial variations. Using results from a recent study of North Atlantic Deep Water (NADW) circulation sensitivity to freshwater forcing and assuming a steady Greenland ice volume, iceberg meltwater forcing is insufficient during interglacial conditions to produce even a partial NADW collapse.
Iceberg
Meltwater
Forcing (mathematics)
Cite
Citations (23)
ABSTRACT A Holocene paleoclimate record was constructed using two lacustrine cores from the high‐elevation Chilean Andes at ∼30°S latitude. Coarser and more poorly sorted grain‐size distributions and higher C/N ratios were interpreted as evidence for increased storm activity. Wet conditions prevailed from ∼10.8 to 9.5k cal a BP, then transitioned to dry conditions from ∼9.5 to 5.7k cal a BP interrupted by stormy conditions from ∼8.3 to 7.6k cal a BP. Wet conditions returned from ∼5.7k cal a BP to the present, interrupted by aridity from ∼4.1 to 2.2k cal a BP. This paleoclimate record is consistent with others from the region. The wet periods were probably caused by the influence of the Southern Westerlies, while dry conditions resulted from the influence of the Southeast Pacific Anticyclone. The increased storminess from ∼8.3 to 7.7k cal a BP may have been sourced from latitudinal shifts in the Intertropical Convergence Zone and subsequent weakening of the Westerlies, allowing the incursion of convective storms from east of the Andes. This sequence of events is consistent with synoptic conditions during modern easterly sourced storm activity. It is also consistent with modeling studies of the effect on the Southern Hemisphere of the rapid cooling of the North Atlantic Ocean during the 8.2‐ka event.
Westerlies
Paleoclimatology
Intertropical Convergence Zone
Anticyclone
Cite
Citations (18)
Low-salinity meltwater from Arctic sea ice and its snow cover accumulates and creates under-ice meltwater layers below sea ice. These meltwater layers can result in the formation of new ice layers, or false bottoms, at the interface of this low-salinity meltwater and colder seawater. As part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we used a combination of sea ice coring, temperature profiles from thermistor strings and underwater multibeam sonar surveys with a remotely operated vehicle (ROV) to study the areal coverage and temporal evolution of under-ice meltwater layers and false bottoms during the summer melt season from mid-June until late July. ROV surveys indicated that the areal coverage of false bottoms for a part of the MOSAiC Central Observatory (350 by 200 m2) was 21%. Presence of false bottoms reduced bottom ice melt by 7–8% due to the local decrease in the ocean heat flux, which can be described by a thermodynamic model. Under-ice meltwater layer thickness was larger below first-year ice and thinner below thicker second-year ice. We also found that thick ice and ridge keels confined the areas in which under-ice meltwater accumulated, preventing its mixing with underlying seawater. While a thermodynamic model could reproduce false bottom growth and melt, it could not describe the observed bottom melt rates of the ice above false bottoms. We also show that the evolution of under-ice meltwater-layer salinity below first-year ice is linked to brine flushing from the above sea ice and accumulating in the meltwater layer above the false bottom. The results of this study aid in estimating the contribution of under-ice meltwater layers and false bottoms to the mass balance and salt budget for Arctic summer sea ice.
Meltwater
Melt pond
Fast ice
Iceberg
Ice divide
Cite
Citations (23)