scholarly journals Radiocarbon and stable isotope constraints on Last Glacial Maximum and Younger Dryas ventilation in the western North Atlantic

2004 ◽  
Vol 19 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Lloyd D. Keigwin
Keyword(s):  
Stable Isotope ◽  
Last Glacial Maximum ◽  
North Atlantic ◽  
Younger Dryas ◽  
Glacial Maximum ◽  
Last Glacial

Last-glacial-maximum North Atlantic deep water: on, off or somewhere in-between?

1995 ◽  
Vol 348 (1324) ◽  
pp. 243-253 ◽  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Deep Water ◽  
Younger Dryas ◽  
Glacial Maximum ◽  
Nutrient Concentrations ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Intermediate Waters

Various papers have been published during the past decade concerning Last Glacial Maximum (LGM) North Atlantic Deep Water (NADW) flow. Using somewhat different methods, they have produced somewhat contradictory results. This review considers both apparent and real conflicts concerning the data and their interpretation, and attempts to resolve them. Despite the earlier (contradictory) interpretations, currently there is a widespread belief that nutrient concentrations in deep cores from the North Atlantic increased during glacial times and that concentrations in the upper-deep and intermediate waters decreased at least slightly. It is also clear that further north in the basin (particularly at upper-deep and intermediate depths), nutrient concentrations were as low or perhaps even lower than those seen today. Data from the Caribbean Sea, ventilated by intermediate waters through an approximately 1800 m sill, indicate that lower nutrient levels were also found at intermediate depths in the North and Tropical Atlantic; this data is supported by continental margin data. The recontoured 8 13 C data of Duplessy et al. ( Paleoceanography 3, 343—360 (1988)) remain a valid expression of the broadscale LGM Atlantic nutrient distribution. Data from the South Atlantic has been the most contradictory to date, but recent 8 13 c evidence from a low-productivity South Atlantic site supports Cd data indicating a relative stability in the nutrient chemistry of waters that are presently influenced by low-nutrient NADW. Sedimentary 231 Pa/ 230 Th data appear to require the continued export of Atlantic-generated 231 Pa from the Atlantic into the Southern Ocean. Finally, radiocarbon evidence from paired planktonic/benthic foraminifera indicates that the ventilation time of the North Atlantic remained low and that the ventilation time of the entire ocean did not change much beyond the uncertainty of the 14 C data. Taken together, this evidence suggests that the NADW became ‘Glacial North Atlantic Deep/Intermediate Water’ (GNAIDW) during glacial times, with perhaps a greater flux through intermediate waters than currently combined with a lesser flux through deeper waters. Although one cannot say much with confidence about the total GNAIDW flux, the data are consistent with a persistent but perhaps somewhat diminished role for NADW in the global thermohaline circulation during glacial times. A review of recent evidence concerning the response of the deep North Atlantic during the Younger Dryas concludes that there is no inconsistency between the new evidence and the occurence of a Younger Dryas NADW event in the deep western North Atlantic.

scholarly journals More efficient North Atlantic carbon pump during the Last Glacial Maximum

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
J. Yu ◽  
L. Menviel ◽  
Z. D. Jin ◽  
D. J. R. Thornalley ◽  
G. L. Foster ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Carbon Pump ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Reconstruction of sea-surface temperature, salinity, and sea-ice cover in the northern North Atlantic during the last glacial maximum based on dinocyst assemblages

2000 ◽  
Vol 37 (5) ◽  
pp. 725-750 ◽  
Author(s):  
Anne de Vernal ◽  
Claude Hillaire-Marcel ◽  
Jean-Louis Turon ◽  
Jens Matthiessen
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Last Glacial Maximum ◽  
North Atlantic ◽  
Ice Cover ◽  
Glacial Maximum ◽  
Sea Surface ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Past sea-surface conditions over the northern North Atlantic during the last glacial maximum were examined from the study of 61 deep-sea cores. The last glacial maximum time slice studied here corresponds to an interval between Heinrich layers H2 and H1, and spanning about 20-16 ka on a 14C time scale. Transfer functions based on dinocyst assemblages were used to reconstruct sea-surface temperature, salinity, and sea-ice cover. The results illustrate extensive sea-ice cover along the eastern Canadian margins and sea-ice spreading, only during winter, over most of the northern North Atlantic. On the whole, much colder winter prevailed, despite relatively mild conditions in August (10-15°C at most offshore sites), thus suggesting a larger seasonal contrast of temperatures than today. Lower salinity than at present is reconstructed, especially along the eastern Canadian and Scandinavian margins, likely because of meltwater supply from the surrounding ice sheets. These reconstructions contrast with those established by CLIMAP on the basis of planktonic foraminifera. These differences are discussed with reference to the stratigraphical frame of the last glacial maximum, which was not the coldest phase of the last glacial stage. The respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses, which was apparently much more stratified than at present in the northern North Atlantic, thus preventing deep-water formation.

scholarly journals Μελέτη των μικροθηλαστικών των τεταρτογενών αποθέσεων του σπηλαίου Α των Λουτρών Αλμωπίας Πέλλας

2013 ◽  
Author(s):  
Αικατερίνη Χατζοπούλου
Keyword(s):  
Last Glacial Maximum ◽  
Younger Dryas ◽  
Glacial Maximum ◽  
Lepus Timidus ◽  
Arvicola Terrestris ◽  
Last Glacial

Στην παρούσα διατριβή μελετήθηκαν τα μικρά θηλαστικά από δύο θέσεις του Σπηλαίου Λουτρών Αλμωπίας. Πρόκειται για έναν απολιθωματοφόρο ορίζοντα στα ιζήματα του δαπέδου του σπηλαίου (θέση LAC) και έναν ορίζοντα που βρίσκεται σε υπερυψωμένο θάλαμο (θέση LAC Ia). Μετά από λεπτομερή ανασκαφική διαδικασία και επεξεργασία των ιζημάτων βρέθηκε πληθώρα δοντιών και οστών μικροθηλαστικών. O προσδιορισμός βασίστηκε στα μορφολογικά και μετρικά χαρακτηριστικά 3209 δειγμάτων. Συνολικά προσδιορίστηκαν 30 διαφορετικά είδη μικροθηλαστικών, εκ των οποίων 29 είδη (8 Εντομοφάγα, 19 τρωκτικά, 2 λαγόμορφα) στη θέση LAC και 26 είδη (6 Εντομοφάγα, 17 τρωκτικά, 3 λαγόμορφα) στη θέση LAC Ia. Επτά από τα είδη που βρέθηκαν στο σπήλαιο Λουτρών Αλμωπίας προσδιορίζονται για πρώτη φορά σε απολιθωμένες πανίδες της Ελλάδας και άλλα επτά είδη δεν αναφέρονται στη σύγχρονη πανίδα της Ελλάδας. Οι πανίδες LAC και LAC Ia χρονολογούνται ως νεότερες της τελευταίας μεσοπαγετώδους περιόδου Riss-Würm από την παρουσία του Arvicola terrestris και παλαιότερες του Ολοκαίνου από την παρουσία του Ochotona pusilla. Ειδικότερα, η πανίδα LAC μπορεί να είναι σύγχρονη ή λίγο νεότερη της πανίδας των μεγάλων θηλαστικών του δαπέδου του σπηλαίου αντιπροσωπεύοντας το Μέσο Würm ως Last Glacial Maximum, ενώ η πανίδα LAC Ia είναι νεότερη αντιπροσωπεύοντας το Younger Dryas. Η σύνθεση των πανίδων LAC και LAC Ia φανερώνει ότι έζησαν σε περιπαγετώδεις συνθήκες, πιο ήπιες από τις τυπικές των Άλπεων κατά την τελευταία παγετώδη περίοδο. Η σύγκριση των ποσοστών συμμετοχής των ειδών δείχνει ότι η πανίδα LAC έζησε σε θερμότερες συνθήκες από την πανίδα LAC Ia. Η παρουσία του Lepus timidus στο θάλαμο LAC Ia σχετίζεται με το μέγιστο ψύχος στο τέλος της τελευταίας Παγετώδους περιόδου και αποτελεί τη νοτιότερη καταγραφή του είδους στην Ευρώπη. Από τις περιβαλλοντικές προτιμήσεις των ειδών που μελετήθηκαν προκύπτει ότι στην ευρύτερη περιοχή υπήρχαν κωνοφόρα και φυλλοβόλα δάση, λειμώνες και αρκετές συγκεντρώσεις νερού. Το κλίμα ήταν ξηρότερο από το σημερινό. Η ταφονομική μελέτη έδειξε ότι τα μικροθηλαστικά των δύο πανίδων αποτέλεσαν τη λεία θηρευτών (μπούφου, πετρίτη και κάποιου σαρκοφάγου θηλαστικού) και συγκεντρώθηκαν μέσα στο σπήλαιο με pellets ή περιττώματα του θηρευτή και τη δράση του νερού. Η μελέτη των ιζημάτων έδειξε ότι πρόκειται για ποτάμιες αποθέσεις με εμφανή επεισόδια έντονων υδραυλικών συνθηκών που αποτέθηκαν κοντά στην πηγή προέλευσής τους.

scholarly journals Extratropical cyclones over the North Atlantic and western Europe during the Last Glacial Maximum and implications for proxy interpretation

2020 ◽  
Vol 16 (2) ◽  
pp. 611-626 ◽  
Author(s):  
Joaquim G. Pinto ◽  
Patrick Ludwig
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Western Europe ◽  
Dust Storms ◽  
Glacial Maximum ◽  
Extratropical Cyclones ◽  
Last Glacial ◽  
The North ◽  
Dominant Feature ◽  
The North Atlantic

Abstract. Extratropical cyclones are a dominant feature of the midlatitudes, as their passage is associated with strong winds, precipitation and temperature changes. The statistics and characteristics of extratropical cyclones over the North Atlantic region exhibit some fundamental differences between pre-industrial (PI) and Last Glacial Maximum (LGM) climate conditions. Here, the statistics are analysed based on results of a tracking algorithm applied to global PI and LGM climate simulations. During the LGM, both the number and the intensity of detected cyclones were higher compared to PI. In particular, increased cyclone track activity is detected close to the Laurentide ice sheet and over central Europe. To determine changes in cyclone characteristics, the top 30 extreme storm events for PI and LGM have been simulated with a regional climate model and high resolution (12.5 km grid spacing) over the eastern North Atlantic and western Europe. Results show that LGM extreme cyclones were characterised by weaker precipitation, enhanced frontal temperature gradients and stronger wind speeds than PI analogues. These results are in line with the view of a colder and drier Europe, characterised by little vegetation and affected by frequent dust storms, leading to reallocation and build-up of thick loess deposits in Europe.

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