Combined Marine Proxy and Pollen Analyses Reveal Rapid Iberian Vegetation Response to North Atlantic Millennial-Scale Climate Oscillations

2001 ◽  
Vol 56 (1) ◽  
pp. 128-132 ◽  
Author(s):  
Katherine H. Roucoux ◽  
Nicholas J. Shackleton ◽  
Lucia de Abreu ◽  
Joachim Schönfeld ◽  
Polychronis C. Tzedakis
Keyword(s):  
North Atlantic ◽  
Phase Relationship ◽  
Deep Sea Sediment ◽  
Climatic Oscillations ◽  
The North ◽  
Tree Population ◽  
North Atlantic Climate ◽  
First Time ◽  
Millennial Scale

AbstractA deep-sea sediment core from the western Portuguese margin has provided a continuous, high-resolution record of millennial-scale climatic oscillations during the interval 9000–65,000 yr B.P. Pollen analysis of the same sequence allows direct, in situ assessment of the phase relationship between the North Atlantic climate system and vegetation changes on the adjacent landmass. This demonstrates for the first time that variability in NW Iberian tree population size closely tracked millennial-scale climate variability.

scholarly journals North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Martin Edwards ◽  
Pierre Hélaouët ◽  
Eric Goberville ◽  
Alistair Lindley ◽  
Geraint A. Tarling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Range Shift ◽  
The Core ◽  
Krill Abundance ◽  
The North ◽  
Living Space ◽  
Warming Climate ◽  
Two Temperatures ◽  
The North Atlantic

AbstractIn the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show, however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a ‘habitat squeeze’, with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that, as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the ‘Atlantification’ of the sub-Arctic.

scholarly journals Glacial fluctuations of the Indian monsoon and their relationship with North Atlantic climate: new data and modelling experiments

2013 ◽  
Vol 9 (5) ◽  
pp. 2135-2151 ◽  
Author(s):  
C. Marzin ◽  
N. Kallel ◽  
M. Kageyama ◽  
J.-C. Duplessy ◽  
P. Braconnot
Keyword(s):  
North Atlantic ◽  
Bay Of Bengal ◽  
Indian Monsoon ◽  
Hydrological Cycle ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The North ◽  
North Atlantic Climate ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract. Several paleoclimate records such as from Chinese loess, speleothems or upwelling indicators in marine sediments present large variations of the Asian monsoon system during the last glaciation. Here, we present a new record from the northern Andaman Sea (core MD77-176) which shows the variations of the hydrological cycle of the Bay of Bengal. The high-resolution record of surface water δ18O dominantly reflects salinity changes and displays large millennial-scale oscillations over the period 40 000 to 11 000 yr BP. Their timing and sequence suggests that events of high (resp. low) salinity in the Bay of Bengal, i.e. weak (resp. strong) Indian monsoon, correspond to cold (resp. warm) events in the North Atlantic and Arctic, as documented by the Greenland ice core record. We use the IPSL_CM4 Atmosphere-Ocean coupled General Circulation Model to study the processes that could explain the teleconnection between the Indian monsoon and the North Atlantic climate. We first analyse a numerical experiment in which such a rapid event in the North Atlantic is obtained under glacial conditions by increasing the freshwater flux in the North Atlantic, which results in a reduction of the intensity of the Atlantic meridional overturning circulation. This freshwater hosing results in a weakening of the Indian monsoon rainfall and circulation. The changes in the continental runoff and local hydrological cycle are responsible for an increase in salinity in the Bay of Bengal. This therefore compares favourably with the new sea water δ18O record presented here and the hypothesis of synchronous cold North Atlantic and weak Indian monsoon events. Additional sensitivity experiments are produced with the LMDZ atmospheric model to analyse the teleconnection mechanisms between the North Atlantic and the Indian monsoon. The changes over the tropical Atlantic are shown to be essential in triggering perturbations of the subtropical jet over Africa and Eurasia, that in turn affect the intensity of the Indian monsoon. These relationships are also found to be valid in additional coupled model simulations in which the Atlantic meridional overturning circulation (AMOC) is forced to resume.

scholarly journals Mode transitions in Northern Hemisphere Glaciation: Co-evolution of millennial and orbital variability in Quaternary climate

2016 ◽  
Author(s):  
David A. Hodell ◽  
James E.T. Channell
Keyword(s):  
Climate Variability ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Ice Sheets ◽  
Deep Ocean ◽  
Progressive Increase ◽  
The North ◽  
Quaternary Climate ◽  
Mode Transitions ◽  
Millennial Scale

Abstract. We present a 3.2-Myr record of stable isotopes and physical properties at IODP Site U1308 (re-occupation of DSDP Site 609) located within the ice-rafted detritus (IRD) belt of the North Atlantic. We compare the isotope and lithological proxies at Site U1308 with other North Atlantic records (e.g., Sites 982, 607/U1313 and U1304) to reconstruct the history of orbital and millennial-scale climate variability during the Quaternary. The Site U1308 record documents a progressive increase in the intensity of Northern Hemisphere glacial-interglacial cycles during the late Pliocene and Quaternary with mode transitions at ~ 2.7, 1.5, 0.9 and 0.65 Ma. These transitions mark times of change in the growth and stability of Northern Hemisphere ice sheets. They also coincide with increases in vertical carbon isotope gradients between the intermediate and deep ocean, suggesting changes in deep carbon storage and atmospheric CO2. Orbital and millennial climate variability co-evolved during the Quaternary such that the trend towards larger ice sheets was accompanied by changes in the style, frequency and intensity of millennial-scale variability. This co-evolution may be important for explaining the observed patterns of Quaternary climate change.

scholarly journals The seasonal cycle of δ<sup>3</sup>C<sub>DIC</sub> in the North Atlantic subpolar gyre

2014 ◽  
Vol 11 (6) ◽  
pp. 1683-1692 ◽  
Author(s):  
V. Racapé ◽  
N. Metzl ◽  
C. Pierre ◽  
G. Reverdin ◽  
P. D. Quay ◽  
...  
Keyword(s):  
North Atlantic ◽  
Dissolved Inorganic Carbon ◽  
Ocean Dynamics ◽  
Subpolar Gyre ◽  
The North ◽  
Winter Convection ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic ◽  
First Time ◽  
Negative Linear Relationship

Abstract. This study introduces for the first time the δ13CDIC seasonality in the North Atlantic subpolar gyre (NASPG) using δ13CDIC data obtained in 2005–2006 and 2010–2012 with dissolved inorganic carbon (DIC) and nutrient observations. On the seasonal scale, the NASPG is characterized by higher δ13CDIC values during summer than during winter, with a seasonal amplitude between 0.70 ± 0.10‰ (August 2010–March 2011) and 0.77 ± 0.07‰ (2005–2006). This is mainly attributed to photosynthetic activity in summer and to a deep remineralization process during winter convection, sometimes influenced by ocean dynamics and carbonate pumps. There is also a strong and negative linear relationship between δ13CDIC and DIC during all seasons. Winter data also showed a large decrease in δ13CDIC associated with an increase in DIC between 2006 and 2011–2012, but the observed time rates (−0.04‰ yr−1and +1.7 μmol kg−1 yr−1) are much larger than the expected anthropogenic signal.

scholarly journals The CORA 5.2 dataset: global in-situ Temperature and Salinity measurements dataset. Data description and validation

2019 ◽  
Author(s):  
Tanguy Szekely ◽  
Jérôme Gourrion ◽  
Sylvie Pouliquen ◽  
Gilles Reverdin
Keyword(s):  
Real Time ◽  
North Atlantic ◽  
Objective Analysis ◽  
Atlantic Basin ◽  
Ocean Variability ◽  
The North ◽  
Error Bar ◽  
The North Atlantic ◽  
Delayed Time

Abstract. We present the Copernicus in-situ ocean dataset of temperature and salinity (version V5.2). The ocean subsurface sampling varied widely from 1950 to 2017, as a result of changes in the instrument technology and development of in-situ observational networks (in particular, tropical moorings, ARGO program). The global ocean temperature data coverage on an annual basis grows thus from 10 % in 1950 (30 % for the North Atlantic basin) to 25 % in 2000 (60 % for the North Atlantic basin) and reaches a plateau exceeding 80 % (95 % for the North Atlantic Ocean) after the deployment of the ARGO program. The average depth reached by the profiles also increases from 1950 to 2017. The validation framework is presented, and an objective analysis-based method is developed to assess the quality of the dataset validation process. Analyses of the ocean variability are calculated without taking into account the data quality flags (raw dataset OA), with the near real time quality flags (NRT dataset OA) and with the delayed time mode quality flags (CORA dataset OA). The comparison of the objective analysis variability shows that the near real time dataset managed to detect and to flag most of the large measurement errors, reducing the analysis error bar compared to the raw dataset error bar. It also shows that the ocean variability of the delayed time mode validated dataset is almost exempt from the random error induced variability.

New species, occurrence records and observations of predation by deep-sea Asteroidea (Echinodermata) from the North Atlantic by NOAA ship Okeanos Explorer

Zootaxa ◽  
2020 ◽  
Vol 4766 (2) ◽  
pp. 201-260 ◽  
Author(s):  
CHRISTOPHER L. MAH
Keyword(s):  
North Atlantic ◽  
Deep Sea ◽  
Substantial Contribution ◽  
The North ◽  
In Situ Observations ◽  
The North Atlantic ◽  
Feeding Observations ◽  
Occurrence Records ◽  
In Situ Feeding

Exploratory cruises by the NOAA Ship Okeanos Explorer have resulted in a substantial contribution in our understanding of deep-sea echinoderm biodiversity, biology, and ecology in the North Atlantic. This includes the description and in situ feeding observations of two, new corallivorous goniasterid species, Evoplosoma nizinskiae n. sp. and Sibogaster bathyheuretor n. sp. Significant in situ observations include a synchronous feeding event including multiple goniasterid asteroids and a cidaroid urchin on a large demosponge, providing new data for understanding echinoderm feeding behavior, including agonistic behavior, in deep-sea settings and new, in situ feeding observations for 28 deep-sea species including the myxasterid Pythonaster atlantidis, the korethrasterid Remaster palmatus and the poorly understood hippasterine goniasterids, Gilbertaster caribaea and Sthenaster emmae. 

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