Volume transport time series and variability of the North Atlantic Eastern Boundary Current at Goban Spur

Since 2016 a moored observatory is operated at the eastern extension of the &#8220;North Atlantic Changes (NOAC)&#8221; array at 47&#176;/48&#176;N. This observatory is installed across the shelf break at Goban Spur and consists of two deep-sea moorings that are separated by about 60 km.&#160;&#160;The aim of this ongoing monitoring program is to quantify the variability and trends in the properties and transport rates of water masses that are advected northwards along the North Atlantic Eastern Boundary and modify the adjacent regions, i.e. the Northwest European Shelf, North Sea, Nordic Seas and Arctic Ocean. Furthermore, the continuous long term time series are essential for a thorough understanding of the circulation system in the eastern North Atlantic and the underlying physical mechanisms that govern its variability.Here, we present results of the analysis of temperature, salinity and current velocity time series from 2016 to 2019. These provide a descriptive view of the complex current structure and variability of water masses on daily to intra- and inter-annual time scales.The most pronounced signal in the variability of temperature and salinity is caused by the presence of Mediterranean Outflow Water located at about 1000 m depth. During the observation period we find significant positive trends in temperature and salinity in the depth range of 500 to 1500 m. The velocity measurements of the onshore mooring show a northeastward directed mean flow following the topography with along-slope variations, while the flow at the offshore mooring position is more unstable with predominantly cross-slope variations.&#160;The combination of our observations with float and altimeter data indicates that the presence of eddies and the interaction with the topography seems to play a crucial role for setting the variability of the flow in this region.Finally, we present an approach to evaluate the volume fluxes at the eastern boundary that will add toward an integrated estimate of the strength of the Atlantic Meridional Overturning Circulation at 47&#176;/48&#176;N.

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

Journal of Climate ◽

10.1175/jcli-d-21-0212.1 ◽

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.

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Variations in mid-latitude North Atlantic surface water properties during the mid-Brunhes (MIS 9–14) and their implications for the thermohaline circulation

Climate of the Past ◽

10.5194/cp-6-531-2010 ◽

2010 ◽

Vol 6 (4) ◽

pp. 531-552 ◽

Cited By ~ 75

Author(s):

A. H. L. Voelker ◽

T. Rodrigues ◽

K. Billups ◽

D. Oppo ◽

J. McManus ◽

...

Keyword(s):

Surface Water ◽

North Atlantic ◽

Current System ◽

Middle Pleistocene ◽

Boundary Current ◽

Upwelling System ◽

The North ◽

Eastern Boundary ◽

Stable Conditions ◽

Hydrographic Conditions

Abstract. Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9–14 (300–540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north – south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.

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