scholarly journals Glacial–interglacial Nd isotope variability of North Atlantic Deep Water modulated by North American ice sheet

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Ning Zhao ◽  
Delia W. Oppo ◽  
Kuo-Fang Huang ◽  
Jacob N. W. Howe ◽  
Jerzy Blusztajn ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Water ◽  
North American ◽  
Isotope Composition ◽  
Ice Sheet ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
Nd Isotope ◽  
Nd Isotope Composition

AbstractThe Nd isotope composition of seawater has been used to reconstruct past changes in the contribution of different water masses to the deep ocean. In the absence of contrary information, the Nd isotope compositions of endmember water masses are usually assumed constant during the Quaternary. Here we show that the Nd isotope composition of North Atlantic Deep Water (NADW), a major component of the global overturning ocean circulation, was significantly more radiogenic than modern during the Last Glacial Maximum (LGM), and shifted towards modern values during the deglaciation. We propose that weathering contributions of unradiogenic Nd modulated by the North American Ice Sheet dominated the evolution of the NADW Nd isotope endmember. If water mass mixing dominated the distribution of deep glacial Atlantic Nd isotopes, our results would imply a larger fraction of NADW in the deep Atlantic during the LGM and deglaciation than reconstructed with a constant northern endmember.

scholarly journals Publisher Correction: Glacial–interglacial Nd isotope variability of North Atlantic Deep Water modulated by North American ice sheet

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ning Zhao ◽  
Delia W. Oppo ◽  
Kuo-Fang Huang ◽  
Jacob N. W. Howe ◽  
Jerzy Blusztajn ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
North American ◽  
Ice Sheet ◽  
North Atlantic Deep Water ◽  
Nd Isotope

Widespread ice sheet retreat in southern Greenland associated with northward expansion and warming of North Atlantic subtropical water masses

2021 ◽  
Author(s):  
Antoon Kuijpers ◽  
Camilla S. Andresen ◽  
Antje H. L. Voelker
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Water Masses ◽  
Subsurface Water ◽  
Mode Water ◽  
Subtropical Water ◽  
Northward Expansion ◽  
Eastern North Atlantic

<p>In the past decades a northward expansion of North Atlantic subtropical water masses<sup>1-3</sup> and warming of subtropical mode water<sup>4,5</sup> (350 – 400 m depth) has been observed. Paleoceanographic records from interglacials prior to 400 ka (‘early Brunhes ‘) reveal a marked inter-hemispheric climate asymmetry with  the average position of the ocean subtropical front in the eastern North Atlantic having shifted at least 4<sup>o</sup> latitude to the north<sup>6,7</sup>. Northward displacement of climate and vegetation belts and previously inferred reduction in sea ice cover at northern high latitudes<sup>7</sup> has later been confirmed by modelling studies<sup>8</sup>. North Atlantic ocean circulation was characterized by an enhanced eastern boundary current poleward transport of warm, (sub)tropical  water masses both at surface and subsurface depth<sup>9,10</sup>.  In recent years (paleo)oceanographic studies of Greenland fjords<sup>  </sup>have demonstrated  that ‘warm’ and saline subsurface water masses of subtropical origin are responsible for sub-glacial melting processes  of Greenland  tide- water glaciers<sup>11-13</sup>. In periods of the early Brunhes interglacials (MIS 11, 13, 15) during which the eastern North Atlantic was characterized by enhanced northward transport of warm, (sub)tropical water masses<sup>9,10</sup>, large parts of the southern Greenland Ice Sheet had melted away and a boreal forest could develop here<sup>14,15</sup> . We conclude that at that time the presence of much warmer, subtropical water masses at subsurface depth in Greenland fjords combined with advection of warm, subtropical air masses with increased precipitation potential from the expanded ocean subtropical gyre region had been responsible for widespread melting of the southern Greenland Ice Sheet. Presently, ongoing  northward expansion and warming of North Atlantic subtropical water masses must therefore be considered to be a process leading to further acceleration of widespread melting of the  (southern) Greenland Ice Sheet.    </p><ul><li>1)   Polovina, J.J. et al. 2008. Geophys. Res. Lett. 35 (3), doi:10.1029/2007GL031745</li> <li>2)   Frundt, B. et al. 2013. Progr. Oceanogr. 116, 246-260, doi:10.1016/j.pocean.2013.07.004</li> <li>3)   Yang, H. et al. 2020. Geophys. Res. Lett. 47 (5), doi:10.1029/2019GL085868</li> <li>4)   Sugimoto, S. et al. 2017. Nature Clim. Change 7, 656-658, doi:10.1038/nclimate3371</li> <li>5)   Wu, L. et al. 2012. Nature Change 2, 161-166, doi:10.1038/nclimate1353</li> <li>6)   Jansen, J.H.F. 1986. Science 232, 619-622</li> <li>7)   Kuijpers, A. Palaeogeogr., Palaeoclimat., Palaeoecol. 76, 67-83</li> <li>8)   Kleinen, T. et al. 2014. Quat. Intern. 348, 247-265, doi:10.1016/j.quaint.2013.12.028</li> <li>9)   Volker, A.H.L. et al. 2010. Clim. Past, 6, 531–552,doi:10.5194/cp-6-531-2010</li> <li>10) Maiorano, P. et al. 2015. Glob. Change 133, 35-48. doi:10.1016/j.glopacha.2015.07.009</li> <li>11) Straneo, F., Heimbach, P. 2013. Nature 504, 36-43</li> <li>12) Adresen, C.S. et al. 2011. The Holocene 21(2), 211-224, doi:10.1177/0959683610378877</li> <li>13) Andresen, C.S. et al. 2013. Shelf. Res. 71, 45-51, doi:10.1016/j.cst.2013.10.003</li> <li>14) Willerslev, E. et al., 2007. Science 317 (5834), 111-114</li> <li>15) De Vernal, A. and Hillaire-Marcel, C., 2008. Science 320, 1622-1625</li> </ul>

scholarly journals Changes in North Atlantic Deep Water strength and bottom water masses during Marine Isotope Stage 3 (45–35kaBP)

2010 ◽  
Vol 29 (19-20) ◽  
pp. 2451-2461 ◽  
Author(s):  
Marcus Gutjahr ◽  
Babette A.A. Hoogakker ◽  
Martin Frank ◽  
I. Nicholas McCave
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Bottom Water ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
Marine Isotope Stage ◽  
Marine Isotope Stage 3

scholarly journals Viral infection of prokaryotic plankton during early formation of the North Atlantic Deep Water

2020 ◽  
Vol 84 ◽  
pp. 175-189
Author(s):  
MG Weinbauer ◽  
C Griebler ◽  
HM van Aken ◽  
GJ Herndl
Keyword(s):  
Viral Infection ◽  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
Life Strategy ◽  
Viral Abundance ◽  
The North ◽  
Early Formation ◽  
The North Atlantic

Viral abundance was assessed in different water masses of the NW Atlantic, and the development of viral abundance, lytic viral infection and lysogeny was followed for the first ca. 5000 km (corresponding to ca. 50 yr in the oceanic conveyor belt) of the western branch of the North Atlantic Deep Water (NADW). Viral abundance was significantly higher in the 100 m layer than in the NADW (2400-2700 m depth) and the Denmark Strait Overflow Water (2400-3600 m depth). The virus-to-prokaryote ratio (VPR) increased with depth, ranging from 32-43 for different water masses of the bathypelagic ocean, thus corroborating the enigma of high viral abundance in the dark ocean. The O2-minimum layer (250-600 m) also showed high viral abundance and VPRs. Viral abundance, a viral subgroup and VPRs decreased in a non-linear form with distance from the NADW origin. Viral production (range: 0.2-2.4 × 107 viruses l-1) and the fraction of lytically infected cells (range: 1-22%) decreased with increasing distance from the formation site of the NADW. Conservative estimations of virus-mediated mortality of prokaryotes in the NADW averaged 20 ± 12%. The fraction of the prokaryotic community with lysogens (i.e. harboring a functional viral DNA) in the NADW averaged 21 ± 14%. Hence, we conclude that (1) viral abundance and subgroups differ between water masses, (2) virus-mediated mortality of prokaryotes as well as lysogeny are significant in the dark ocean and (3) the lysogenic life strategy became more important than the lytic life style during the early formation of the NADW.

scholarly journals Dynamics of North Atlantic Deep Water masses during the Holocene

2011 ◽  
Vol 26 (4) ◽  
Author(s):  
Babette A. A. Hoogakker ◽  
Mark R. Chapman ◽  
I. Nick McCave ◽  
Claude Hillaire‐Marcel ◽  
Christopher R. W. Ellison ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
The Holocene

Constraining Mantle Source Conditions at Iceland and Adjoining Ridges Using Markov Chain Monte Carlo Inversion

2020 ◽  
Author(s):  
Eric Brown ◽  
Charles Lesher
Keyword(s):  
Monte Carlo ◽  
Trace Element ◽  
North Atlantic ◽  
Isotope Composition ◽  
Nd Isotope ◽  
The North ◽  
Depleted Mantle ◽  
Heterogeneous Mantle ◽  
The North Atlantic ◽  
Nd Isotope Composition

<p>Basalts are generated by adiabatic decompression melting of the upper mantle, and thus provide spatial and temporal records of the thermal, compositional, and dynamical conditions of their source regions. Uniquely constraining these factors through the lens of melting is challenging given the complexity of the melting process. To limit the <em>a priori</em> assumptions typically required for forward modeling of mantle melting, and to assess the robustness of the modeling results, we combine a Markov chain Monte Carlo sampling method with the forward melting model REEBOX PRO [1] simulating adiabatic decompression melting of lithologically heterogeneous mantle. Using this method, we invert for mantle potential temperature (Tp), lithologic trace element and isotopic composition and abundance, and melt productivity together with a robust evaluation of the uncertainty in these system properties. We have applied this new methodology to constrain melting beneath the Reykjanes Peninsula (RP) of Iceland [2] and here extend the approach to Iceland’s Northern Volcanic Zone (NVZ). We consider melting of a heterogeneous mantle source involving depleted peridotite and pyroxenite lithologies, e.g., KG1, MIX1G and G2 pyroxenites. Best-fit model sources for Iceland basalts contain more than 90% depleted peridotite and less than 10% pyroxenite with Tp ~125-200 °C above ambient mantle. The trace element and Pb and Nd isotope composition of the depleted source beneath the Reykjanes Peninsula is similar to DMM [3], whereas depleted mantle for the NVZ is isotopically distinct and more trace element enriched. Conversely, inverted pyroxenite trace element compositions are similar for RP and NVZ and are more enriched than previously inferred, despite marked differences in their Pb and Nd isotope composition. We use these new constraints on the Iceland source to investigate their relative importance in basalt genesis along the adjoining Reykjanes and Kolbeinsey Ridges. We find that the proportion of pyroxenite diminishes southward along Reykjanes Ridge and is seemingly absent to the north along the Kolbeinsey Ridge. Moreover, abundances of inverted RP and NVZ depleted mantle also diminish away from Iceland and give way to a common depleted source for the North Atlantic. These findings further illuminate the along-strike variability in source composition along the North Atlantic ridge system influenced by the Iceland melting anomaly, while reconciling geochemical, geophysical and petrologic constraints required to rigorously test plume vs. non-plume models.</p><p>[1] Brown & Lesher (2016); G^3, v. 17, p. 3929-2968</p><p><span>[2] Brown et al. (2020); EPSL, v. 532, 116007</span></p><p>[3] Workman and Hart (2005); EPSL, v.231, p. 53-72</p>

scholarly journals Water masses and zonal current in the Western Tropical Atlantic in October 2007 and January 2008 (AMANDES project)

2010 ◽  
Vol 7 (6) ◽  
pp. 1953-1976
Author(s):  
A. C. Silva ◽  
M. Grenier ◽  
R. Chuchla ◽  
J. Grelet ◽  
F. Roubaud ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Lower Layer ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
Western Boundary ◽  
Intermediate Water ◽  
Tropical Atlantic ◽  
The North ◽  
North Brazil

Abstract. The properties and circulation of water masses are examined using data collected from a hydrographic and Acoustic Doppler Current profiler in the Western Tropical Atlantic during two cruises of the GEOTRACES process study "AMANDES" (AMazon-ANDEans): AMANDES I (October–November 2007) and AMANDES II (January 2008). In the upper layer (from the sea surface to 150 m) means of vertical sections of velocity are showing the structure of the Current (NBC) and North Equatorial Countercurrent. In the lower layer (below 150 m) the subsurface velocity core of the North Brazil UnderCurrent, Western Boundary Undercurrent (WBUC) and northern branch of the South Equatorial Current (nSEC) could be observed. In October the WBUC flows southeastward with a velocity of about 0.3 m s−1. In the studied area during October 2007, the NBUC and nSEC are transporting South Atlantic Central Water (SACW) from the Southern Hemisphere whereas the WBUC transports North Atlantic Central Water (NACW) southeastward. In the deep layers, the North Atlantic Deep Water (NADW) is composed of three components: the Upper North Atlantic Deep Water – UNADW (between 1310 and 1650 m), the Middle North Atlantic Deep Water (between 1930 and 2400 m), the Lower North Atlantic Deep Water (centered around 3430 m). Off Guyana, the Antartic Intermediate Water (AAIW) changes of composition between October 2007 (45.2% ACW, 32.2% AAIWsource and 22.6% UNADW) and January 2008 (62.4% ACW, 23.5% AAIWsource and 14.1% UNADW). These intermediate waters are significantly warmer, less oxygenated and saltier than their southern source, reflecting both oxygen consumption and mixing with the Atlantic Central Water (ACW) and the Upper North Atlantic Deep Water during their northward transit.

Sign in / Sign up

Export Citation Format

Share Document