Magnetic observations from the Arctic and North Atlantic oceans

Eos ◽  
1992 ◽  
Vol 73 (11) ◽  
pp. 123-123 ◽  
Author(s):  
R. Macnab ◽  
S. Srivastava
Keyword(s):  
North Atlantic ◽  
The Arctic

scholarly journals Change in the North Atlantic circulation associated with the mid-Pleistocene transition

2018 ◽  
Vol 14 (11) ◽  
pp. 1639-1651 ◽  
Author(s):  
Gloria M. Martin-Garcia ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
Fátima Abrantes
Keyword(s):  
North Atlantic ◽  
Major Change ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
North Atlantic Current ◽  
The North ◽  
Oceanic Fronts ◽  
Surface Circulation ◽  
The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37∘34.285′ N, 10∘7.562′ W; 2585 m b.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55∘ N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100 ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100 ky cycles.

Meridional Tripole Mode of Winter Precipitation over the Arctic and Continental North Africa–Eurasia

2021 ◽  
pp. 1
Author(s):  
Xiaolin Liu ◽  
Jianhua Lu ◽  
Yimin Liu ◽  
Guoxiong Wu
Keyword(s):  
Time Series ◽  
North Africa ◽  
North Atlantic ◽  
Hadley Cell ◽  
The Arctic ◽  
Positive Phase ◽  
The North ◽  
Ferrel Cell ◽  
The North Atlantic ◽  
Westerly Jets

AbstractWintertime precipitation is vital to the growth of glaciers in the northern hemisphere. We find a tripole mode of precipitation (PTM), with each pole of the mode extending zonally over the eastern hemisphere roughly between 30°W and 120°E, and the positive/negative/positive structure for its positive phase extending meridionally from the Arctic to the continental North Africa–Eurasia. The large-scale dynamics associated with the PTM is explored. The positive phase of the PTM is associated with the negative while eastward-shifted phase of the North Atlantic Oscillation (NAO) and a zonal band of positive SST anomaly in the tropics, together with a narrowed Hadley cell and weakened Ferrel cell. While being north-eastward tilted and separated from their North Africa-Eurasia counterpart in the climatological mean, the upper-tropospheric westerly jets over the east Pacific and north Atlantic become extending zonally and shifting southward and hence form a circumpolar subtropical jet as a whole by connecting with the westerly jets over the North Africa-Eurasia. The enhanced zonal winds over the north Atlantic promote more synoptic-scale transient eddies which are waveguided by the jet streams. The polar vortex weakens and cold air dips southward from the North Pole. Further diagnosis of the E-vectors suggests that transient eddies have a positive feedback on the weakening of Ferrel cell. Opposite features are associated with the negative phase of the PTM. The reconstructed time series using multiple linear regression on the NAO index and the tropical SST averaged over 20°S– 20°N, can explain 62.4% of the variance of the original the original precipitation time series.

Propagation of Thermohaline Anomalies and their predictive potential in the Northern North Atlantic

2021 ◽  
Author(s):  
Helene R. Langehaug ◽  
Pablo Ortega ◽  
Francois Counillon ◽  
Daniela Matei ◽  
Elizabeth Maroon ◽  
...  
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
Atlantic Water ◽  
The Arctic ◽  
Lead Times ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Predictive Skill ◽  
Prediction Systems ◽  
Water Pathway

<p>In this study we assess to what extent seven different dynamical prediction systems can retrospectively predict the winter sea surface temperature (SST) in the subpolar North Atlantic and the Nordic Seas in the time period 1970-2005. We focus in particular on the region where warm water flows poleward, i.e., the Atlantic water pathway, and on interannual-to-decadal time scales. To better understand why dynamical prediction systems have predictive skill or lack thereof, we confront them with a mechanism identified from observations – propagation of oceanic anomalies from low to high latitudes – on different forecast lead times. This observed mechanism shows that warm and cold anomalies propagate along the Atlantic water pathway within a certain time frame. A key result from this study is that most models have difficulty representing this mechanism, resulting in an overall poor prediction skill after 1-2 years lead times (after applying a band-pass filter to focus on interannual-to-decadal time scales). There is a link, although not very strong, between predictive skill and the representation of the SST propagation. Observational studies demonstrate predictability several years in advance in this region, thus suggesting a great potential for improvement of dynamical climate predictions by resolving the causes for the misrepresentation of the oceanic link. Inter model differences in simulating surface velocities along the Atlantic water pathway suggest that realistic velocities are important to better circulate anomalies poleward, and hence, increase predictive skill on interannual-to-decadal time scales in the oceanic gateway to the Arctic.</p>

X. NATO and the Challenge in the North Atlantic and the Arctic

2018 ◽  
Vol 93 (1) ◽  
pp. 121-128 ◽  
Author(s):  
James G Foggo ◽  
Alarik Fritz
Keyword(s):  
North Atlantic ◽  
The Arctic ◽  
The North ◽  
The North Atlantic

scholarly journals Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice

2017 ◽  
Vol 59 (76pt2) ◽  
pp. 181-190 ◽  
Author(s):  
Thomas J. Ballinger ◽  
Edward Hanna ◽  
Richard J. Hall ◽  
Thomas E. Cropper ◽  
Jeffrey Miller ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Circulation Pattern ◽  
The Arctic ◽  
Labrador Sea ◽  
First Year ◽  
Tropospheric Circulation ◽  
Blocking Index

ABSTRACTThe Arctic marine environment is undergoing a transition from thick multi-year to first-year sea-ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade−1 earlier from 1979 to 2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013. (~6σ below the 1981–2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI). The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI >+1 on >75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt ~50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.

scholarly journals On the Nonlinearity of Winter Northern Hemisphere Atmospheric Variability

2019 ◽  
Vol 76 (1) ◽  
pp. 333-356 ◽  
Author(s):  
A. Hannachi ◽  
W. Iqbal
Keyword(s):  
North Atlantic ◽  
Polar Vortex ◽  
Principal Component ◽  
Empirical Orthogonal Functions ◽  
The Arctic ◽  
Climate Change Signal ◽  
Two Dimensional ◽  
Orthogonal Functions ◽  
Local Flow ◽  
The North

Abstract Nonlinearity in the Northern Hemisphere’s wintertime atmospheric flow is investigated from both an intermediate-complexity model of the extratropics and reanalyses. A long simulation is obtained using a three-level quasigeostrophic model on the sphere. Kernel empirical orthogonal functions (EOFs), which help delineate complex structures, are used along with the local flow tendencies. Two fixed points are obtained, which are associated with strong bimodality in two-dimensional kernel principal component (PC) space, consistent with conceptual low-order dynamics. The regimes reflect zonal and blocked flows. The analysis is then extended to ERA-40 and JRA-55 using daily sea level pressure (SLP) and geopotential heights in the stratosphere (20 hPa) and troposphere (500 hPa). In the stratosphere, trimodality is obtained, representing disturbed, displaced, and undisturbed states of the winter polar vortex. In the troposphere, the probability density functions (PDFs), for both fields, within the two-dimensional (2D) kernel EOF space are strongly bimodal. The modes correspond broadly to opposite phases of the Arctic Oscillation with a signature of the negative North Atlantic Oscillation (NAO). Over the North Atlantic–European sector, a trimodal PDF is also obtained with two strong and one weak modes. The strong modes are associated, respectively, with the north (or +NAO) and south (or −NAO) positions of the eddy-driven jet stream. The third weak mode is interpreted as a transition path between the two positions. A climate change signal is also observed in the troposphere of the winter hemisphere, resulting in an increase (a decrease) in the frequency of the polar high (low), consistent with an increase of zonal flow frequency.

scholarly journals Arctic–North Atlantic Interactions and Multidecadal Variability of the Meridional Overturning Circulation

2005 ◽  
Vol 18 (19) ◽  
pp. 4013-4031 ◽  
Author(s):  
Johann H. Jungclaus ◽  
Helmuth Haak ◽  
Mojib Latif ◽  
Uwe Mikolajewicz
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Deep Water Formation ◽  
Overturning Circulation ◽  
Multidecadal Variability ◽  
Water Formation ◽  
Meridional Overturning

Abstract Analyses of a 500-yr control integration with the non-flux-adjusted coupled atmosphere–sea ice–ocean model ECHAM5/Max-Planck-Institute Ocean Model (MPI-OM) show pronounced multidecadal fluctuations of the Atlantic overturning circulation and the associated meridional heat transport. The period of the oscillations is about 70–80 yr. The low-frequency variability of the meridional overturning circulation (MOC) contributes substantially to sea surface temperature and sea ice fluctuations in the North Atlantic. The strength of the overturning circulation is related to the convective activity in the deep-water formation regions, most notably the Labrador Sea, and the time-varying control on the freshwater export from the Arctic to the convection sites modulates the overturning circulation. The variability is sustained by an interplay between the storage and release of freshwater from the central Arctic and circulation changes in the Nordic Seas that are caused by variations in the Atlantic heat and salt transport. The relatively high resolution in the deep-water formation region and the Arctic Ocean suggests that a better representation of convective and frontal processes not only leads to an improvement in the mean state but also introduces new mechanisms determining multidecadal variability in large-scale ocean circulation.

scholarly journals North Atlantic deep water formation and AMOC in CMIP5 models

Ocean Science ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 609-622 ◽  
Author(s):  
Céline Heuzé
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Water ◽  
Deep Convection ◽  
The Arctic ◽  
Subpolar Gyre ◽  
Deep Water Formation ◽  
Nordic Seas ◽  
Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.

scholarly journals Upper Proterozoic and Lower Palaeozoic strata in northern East Greenland

1989 ◽  
Vol 145 ◽  
pp. 103-108
Author(s):  
M.J Hambrey ◽  
J.S Peel ◽  
M.P Smith
Keyword(s):  
North Atlantic ◽  
The Arctic ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
East Greenland ◽  
Upper Proterozoic ◽  
Clastic Sediments ◽  
Upper Riphean ◽  
Lower Palaeozoic ◽  
The Subject

The Caledonides of East Greenland contain the best exposures of Upper Riphean to Ordovician sediments in the Arctic - North Atlantic region. At its thickest the sequence contains 13 km of Eleonore Bay Group clastic sediments and carbonates, the 0.8 km thick Tillite Group and 3 km of Cambro-Ordovician strata (Henriksen & Higgins, 1976; Henriksen, 1985). These sediments crop out in a belt stretching for nearly 300 km through the fjord region, between 71° 38' and 74° 25'N. Those in the northern part of the region, between Brogetdal in Strindberg Land and southern Payer Land, and especiaIly Albert Heim Bjerge and C. H. Ostenfeld Nunatak, were the subject of investigation during 1988 (figs 1, 2).

scholarly journals Effect of gas-transfer-velocity parameterization choice on CO<sub>2</sub> air–sea fluxes in the North Atlantic and European Arctic

2015 ◽  
Vol 12 (6) ◽  
pp. 2591-2616
Author(s):  
I. Wróbel ◽  
J. Piskozub
Keyword(s):  
North Atlantic ◽  
World Ocean ◽  
Software Tool ◽  
The Arctic ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Gas Transfer Velocity ◽  
The North ◽  
European Arctic ◽  
The North Atlantic

Abstract. The ocean sink is an important part of the anthropogenic CO2 budget. Because the terrestrial biosphere is usually treated as a residual, understanding the uncertainties the net flux into the ocean sink is crucial for understanding the global carbon cycle. One of the sources of uncertainty is the parameterization of CO2 gas transfer velocity. We used a recently developed software tool, FluxEngine, to calculate monthly net carbon air–sea flux for the extratropical North Atlantic, European Arctic as well as global values (or comparison) using several available parameterizations of gas transfer velocity of different dependence of wind speed, both quadratic and cubic. The aim of the study is to constrain the uncertainty caused by the choice of parameterization in the North Atlantic, a large sink of CO2 and a region with good measurement coverage, characterized by strong winds. We show that this uncertainty is smaller in the North Atlantic and in the Arctic than globally, within 5 % in the North Atlantic and 4 % in the European Arctic, comparing to 9 % for the World Ocean when restricted to functions with quadratic wind dependence and respectively 42, 40 and 67 % for all studied parameterizations. We propose an explanation of this smaller uncertainty due to the combination of higher than global average wind speeds in the North Atlantic and lack of seasonal changes in the flux direction in most of the region. We also compare the available pCO2 climatologies (Takahashi and SOCAT) pCO2 discrepancy in annual flux values of 8 % in the North Atlantic and 19 % in the European Arctic. The seasonal flux changes in the Arctic have inverse seasonal change in both climatologies, caused most probably by insufficient data coverage, especially in winter.

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