On the correlation between oscillations of the Caspian Sea level and the North Atlantic climate

Correlations between the changes in the climate of the Caspian Sea region and in its level and the variations in the North Atlantic climate are studied. The indices of North Atlantic oscillation (NAO), Atlantic multidecadal oscillation (AMO), the intensity of Atlantic thermohaline circulation (ATHC), and the air humidity above the North Atlantic are used as basic indicators of climatic variations that influence the Caspian Sea. Results of an experiment for reproducing the World Ocean circulation and the parameterization of cyclic climate peculiarities made it possible to reveal their impact on the formation of Eurasian climatic variability and on the level regime of the Caspian Sea. This impact is studied through the variability of ATHC, the NAO index, and a composite index of moisture transport (CIMT) that is proposed as a result of the studies.     

The Continuous Plankton Recorder survey and the North Atlantic Oscillation: Interannual- to Multidecadal-scale patterns of phytoplankton variability in the North Atlantic Ocean

At interannual to multidecadal time scales, much of the oceanographic and climatic variability in the North Atlantic Ocean can be associated with the North Atlantic Oscillation (NAO). While evidence suggests that there is a relationship between the NAO and zooplankton dynamics in the North Atlantic Ocean, the phytoplankton response to NAO-induced changes in the environment is less clear. Time series of monthly mean phytoplankton colour values, as compiled by the Continuous Plankton Recorder (CPR) survey, are analysed to infer relationships between the NAO and phytoplankton dynamics throughout the North Atlantic Ocean. While a few areas display highly significant (p < 0.05) trends in the CPR colour time series during the period 1948–2000, nominally significant (p < 0.20) positive trends are widespread across the basin, particularly on the continental shelves and in a transition zone stretching across the Central North Atlantic. When long-term trends are removed from both the NAO index and CPR colour time series, the correlation between them ceases to be significant. Several hypotheses are proposed to explain the observed variability in the CPR colour and its relationship with climate in the North Atlantic.     

Coastline configuration disrupts the effects of large-scale climatic forcing, leading to divergent temporal trends in wave exposure

Both climate change and the North Atlantic Oscillation (NAO) may influence coastal systems by altering wave exposure. The effects of such climatic forcing are often coherent over relatively large geographic areas. Temporal trends in wave exposure at any particular shore are, however, the result of an interaction between site-specific fetch characteristics and changes in wind climate. This leads to contrasting trends in wave exposure at locations separated by no more than a few kilometres. Wave exposures were estimated at locations around a sea lough over 32 years to characterise these scales of variability. Locations separated by approximately 5 km had independent dynamics with respect to the temporal trend (correlation range −0.35 to 0.44) and to associations with the NAO (correlation range −0.18 to 0.40). Wave exposure can therefore be increasing for a section of shore while nearby areas have the opposite trend. Mean exposure at a location was not a good predictor of the temporal trend. More exposed sites were, however, sensitive to variations in the strength of the NAO. The reduction of large scale forcing to small-scale variability has implications for the detection and mitigation of potential climate change impacts.     

Atlantic meridional overturning circulation and phosphate-classified bottom-up control of Atlantic pelagic ecosystems through the 20th century

Both the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Ocean (NA) biosphere have recognized associations with the North Atlantic Oscillation (NAO). These multidecadal physical–biological affinities inspired a closer look at AMOC influences on bottom-up control of NA and South Atlantic Ocean (SA) pelagic ecosystem variability. Various ocean models associate changes in the AMOC with sea surface temperature (SST) differences in the western subpolar NA and SA represented as the Atlantic Dipole SST Anomaly (ADSA) index. The Extended Reconstructed SST version 2 (ERSSTv2) dataset for 2° quadrangles from 1890 to 2007 was used here to represent Atlantic Ocean SST patterns and to gauge 20th century AMOC variability using an Atlantic Dipole SST (ADS) index, an un-normalized version of ADSA index. Temperature–phosphate (T–PO₄) linear regressions were used to convert temperature to phosphate concentration ([PO₄]). The interannual stability of T–PO₄ linear regressions first was examined using 26 Bermuda area T–PO₄ datasets between 1958 and 2001. Within the constraints provided by the Bermuda analysis, climatological T–PO₄ linear regressions based on GEOSECS-derived slopes and NODC-derived X-intercepts supported the conversion of monthly Atlantic Ocean ERSSTv2 temperatures for each 2° quadrangle to monthly surface [PO₄]. A representative annual surface phosphate utilization (SPU) was calculated for each 2° quadrangle by subtracting monthly minimum surface [PO₄] from monthly maximum surface [PO₄] to determine the annual surface [PO₄] ranges from 1890 to 2007. Annual average SST tended to increase and overall annual average SPU tended to decrease through the 20th century in both the NA and SA, but the NA exhibited more temporal variability. An Atlantic Dipole Phosphate Utilization (ADPU) index related to the ADS index was calculated for each year from 1890 to 2007. The ADS and ADPU indices were inversely correlated with about 57% of the variability in the ADPU index explained by the ADS index. The ADPU index exhibited three distinct cycles through the 20th century. Cross-correlation analysis showed that the NAO led the ADS and ADPU indices by about 14 years. Differences in annual average SPU for each Atlantic Ocean 2° quadrangle between the three high and four low years of the ADPU cycles yielded six maps that, when averaged, clearly exhibited reversed east–west patterns distributed in alternating latitudinal bands in both the NA and SA. The east–west patterns spatially corresponded to the NA and SA surface circulation and temporally resembled NA patterns previously associated with the NAO. AMOC variability, mediated by Kelvin and Rossby waves associated with changes in both deep and surface arm circulation, likely contributed to meridional continuity of phosphate-classified, NA, and SA pelagic ecosystem variability, including fisheries, through the 20th century. Based on the results, future global warming influences on the AMOC, well short of shutdown, likely will have complex pelagic ecosystem impacts throughout the Atlantic Ocean.     

Two Modes of Atmosphere–Ocean Interaction in the Atlantic Sector of the Arctic Basin

Oceanology - The paper examines the influence of the main mode of interannual variability of the North Atlantic climate system—the North Atlantic Oscillation (NAO)—on the hydrophysical...     

基于PMIP2气候模式模拟的中全新世北大西洋涛动

根据PMIP2中的4个海气耦合模式对中全新世气候的模拟结果,利用现代和中全新世两个时间段的冬季海平面气压场(SLP),分析了北大西洋海平面气压的变化情况并计算了这两个时间段的北大西洋涛动(NAO)指数。结果表明,中全新世亚速尔高压加强,冰岛低压加深,南北气压差增加,NAO强度显著增强。对中全新世北大西洋地区SLP进行经验正交函数(EOF)分析显示,4个模式均能捕捉到了NAO的主要结构。中全新世NAO处于正位相的时间较现代提高了10%~30%,其中MIROC3.2提高了29.3%;虽然NAO指数振幅变化不大,但还是能显示中全新世NAO显著强于现代,这与地质资料恢复的结果相一致。对NAO指数的多窗谱分析显示,现代NAO指数存在3~5 a的准周期变化,中全新世NAO指数存在3 a的准周期变化。NAO对中全新世亚洲地区冬季增温有重要影响。北大西洋地区中纬度海面温度(SST)的增温可能是导致中全新世NAO强度增强的一个重要因素。     

Ocean acidification in New Zealand waters: trends and impacts

The threat posed by ocean acidification (OA) to the diversity and productivity of New Zealand marine ecosystems is assessed in a synthesis of published trends and impacts. A 20-year time series in Subantarctic water, and a national coastal monitoring programme, provide insight into pH variability, and context for experimental design, modelling and projections. A review of the potential impact of changes in the carbonate system on the major phyla in New Zealand waters confirms international observations that calcifying organisms, and particularly their early life-history stages, are vulnerable. The synthesis considers ecosystem and socio-economic impacts, and identifies current knowledge gaps and future research directions, including mechanistic studies of OA sensitivity. Advanced ecosystem models of OA, that incorporate the indirect effects of OA and interactions with other climate stressors, are required for robust projection of the future status of New Zealand marine ecosystems.     

Role of the Ocean in Maintaining the North-Atlantic Oscillation

Based on the data on the sea-surface temperature (SST), the heat content of the upper 200-m layer, and the sea-level pressure, we analyze the low-frequency variability of the SST and heat content in the North Atlantic in 1950–1992 and the index of North-Atlantic Oscillation (NAO) in 1940–1995. It is confirmed that the role of the ocean and various mechanisms controlling the variability of SST changes for processes corresponding to different time scales (interannual, decadal, and interdecadal). It is shown that the interaction of tropical and subtropical latitudes is of principal importance on the interannual scale, the processes regulating the variability of subtropical gyre are important on the decadal scale, and the variations of the NAO with lower frequencies are controlled by the oceanic variability at high latitudes. We discuss possible feedbacks in the ocean–atmosphere system maintaining the NAO.     

Covariance among North Sea ecosystem state indicators during the past50 years — Contrasts between coastal and open waters

Regime shift and principal component analysis of a spatially disaggregated database capturing time-series of climatic, nutrient and plankton variables in the North Sea revealed considerable covariance between groups of ecosystem indicators. Plankton and climate time-series span the period 1958–2003, those of nutrients start in 1980. In both regions, the period from 1989 to 2001 identified in principal component 1 had warmer surface waters, higher Atlantic inflow and stronger winds, than the periods before or after. However, it was preceded by a regime shift in both open (PC2) and coastal (PC3) waters during 1977 towards more hours of sunlight and higher water temperature, which lasted until 1997. The relative influence of nutrient availability and climatic forcing differed between open and coastal North Sea regions. Inter-annual variability in phytoplankton dynamics of the open North Sea was primarily regulated by climatic forcing, specifically by sea surface temperature, Atlantic inflow and co-varying wind stress and NAO. Coastal phytoplankton variability, however, was regulated by insolation and sea surface temperature, as well as Si availability, but not by N or P. Regime shifts in principal components of hydrographic and climatic variables (explaining 55 and 61% of the variance in coastal and open water variables) were detected using Rodionov's sequential t-test. These shifts in hydroclimatic variables which occurred around 1977, 1989, 1997 and 2001, were synchronized in open and coastal waters, and were tracked by open water chlorophyll and copepods, but not by coastal plankton. North–central–south or open-coastal spatial breakdowns of the North Sea explained similar amounts of variability in most ecosystem indicators with the exception of diatom abundance and chlorophyll concentration, which were clearly better explained using the open-coastal configuration.     

Air pressure fluctuations in the North Atlantic and their relationship with El Niño-southern oscillations

Seasonal and interannual variability of the pressure field and indices of the North Atlantic atmosphere zonal circulation are analysed using historical (1894–1988) observations. It is shown that fluctuations of the index of North Atlantic oscillations (NAO) and that of the eastward transport give evidence of the interannual fluctuations with the typical time scale being 2–7 years. It is shown that the magnitude of interannual NAO index variability exceeds the typical magnitude of seasonal variations, particularly in winter. The time scale of NAO index variations and eastward transport coincides with the typicalEl Niño-southern oscillations (ENSO) temporal scale. The amplitudes of the annual, semi-annual harmonics, and high-frequency fluctuations of the NAO index increase during a typical ENSO event at least by a factor of 2.Translated by V. Puchkin.     

Influence of long-term regional and large-scale atmospheric circulation on the Baltic sea level

The connection between variations in the North Atlantic Oscillation (NAO) index and the Baltic sea level has been investigated for the period 1825–1997. The association between the NAO and the strength of the zonal geostrophic wind stress over the Northwest Atlantic suggests an NAO impact on Baltic sea level variations, because the monthly mean sea level mainly is determined by externally driven variations caused by wind conditions over the North Sea. Several period bands were found to have high correlation between oscillations in the winter (JFM) NAO index and the Baltic Sea winter mean sea level. The correlation was, however, higher in the 20th century than in the 19th. During the last two decades, the correlation between the NAO index and the sea level has been exceptionally high. The winter mean of a regional atmospheric circulation index had a correlation with the Kattegat winter mean sea level of 0.93. With the Baltic sea level the correlation was 0.91, compared with the NAO index correlation for the same period of 0.74. The regional index also showed a high correlation with the mean summer and mean autumn sea levels, when the corresponding seasonal NAO indices showed a weak connection. The temporal variation of the connection with the NAO index implies a regional atmospheric circulation occasionally differing from the large-scale circulation associated with the NAO. Seasonal means of the sea level in Stockholm do, however, reflect the regional wind climate to a large extent, and the Baltic sea level is a useful proxy for identifications of climatic dependencies in the region.     

Study of the mutual influence of the El Niño-Southern Oscillation processes and the North Atlantic and Arctic Oscillations

On the basis of the nonlinear techniques for the estimation of coupling between oscillatory systems from time series, we investigate the dynamics of climatic modes characterizing global and Northern Hemisphere (NH) processes. The North Atlantic Oscillation (NAO) and Arctic Oscillation indices and the El Niño-Southern Oscillation (ENSO) indices are analyzed in terms of the most reliable data from 1950 through 2004 and earlier data since the 19th century. These indices characterize changes in NH atmospheric pressure (specifically, sea-level pressure in the North Atlantic and NH extratropical latitudes as a whole) and in equatorial Pacific sea-surface temperature and sea-level pressure to which the strongest variations of global surface temperature and global climate on interannual time scales and of regional climatic anomalies in the NH are linked. The methods used are based on phase-dynamics modeling and nonlinear prediction models (a nonlinear version of Granger causality). From both methods and various ENSO indices, the inference about the ENSO effect on the NAO during the latter half of the 20th century and in the early 21st century is made with confidence probability of at least 0.95. The influence is characterized by a time delay of about two years. No inverse influence is found with a similar degree of reliability. Results of estimating the coupling between the ENSO and the NAO depend on the type of index that is used to describe the NAO. The ENSO effect on the NAO is detected with sufficient confidence when the NAO index is chosen to be a larger scale characteristic. However, when a more local index of the NAO is used, no statistically significant coupling to the ENSO is found. Increasing the length of the analyzed ENSO and NAO series (over more than 100 yr) does not lead to any more reliable detection of coupling. Analysis of the data for different time intervals during 1950–2004 has revealed a strengthening of the ENSO effect on the NAO, although this inference is not reliable.     

Long-term evolution of Baltic Sea wave climate near a coastal segment in Poland; its drivers and impacts

The paper analyses long-term variability of wave climate near Poland for the 1958–2002 period. With spectral and cross-spectral analysis, linear regression and singular spectrum analysis the modes of long-term variability were quantified for the most energetic months (November–February). For monthly indices of North Atlantic Oscillation from 1950 until 2006, it was established that the long-term trends of NAO and significant wave height demonstrate a gentle coupling. For Januaries this relationship is strongest and dates back to 1960, for Februaries a certain consistency appears since 1975. For Novembers and Decembers no statistically discernible coupling was found. Thus, the Baltic Sea appears to be the easternmost NAO-affected region, despite its separation from the Atlantic. The hydrodynamic variability also includes a non-trivial oscillation in the January wave energy records with T=8 years. The same periodicity was identified with the multi-channel SSA technique in the long-term shoreline data of a neighboring beach. The study shows that even almost entirely isolated water bodies are becoming exposed to global climatic phenomena and accelerated erosion of sandy beaches, typical for the South Baltic region. On the other hand, the 8-year hydrodynamic cycle can be viewed as the driver of long-term shoreline evolution.     

Compound response of marine and terrestrial ecosystems to varying climate: pre-anthropogenic perspective from bivalve shell growth increments and tree-rings

Annual growth increments were examined from shells of the ocean quahog (Arctica islandica L.) from northwest Norway and from tree-ring samples of the Scots pine (Pinus sylvestris L.) from nearby coastal areas. The reconstructed annual growth increments were used to compare growth variability in marine and terrestrial ecosystems. Spatiotemporal comparison of the growth records showed statistically significant correlation during the 19th century A.D., indicative of ecosystem-independent response to pre-anthropogenic climate variations. Geographical correlation between marine and terrestrial records was only observed at the local scale. Years with particularly low winter or high summer North Atlantic Oscillation (NAO) indices showed the best synchronization of marine and terrestrial growth. Despite strong correlation during historical time, our palaeoecological evidence suggests that marine and terrestrial ecosystems may show dissimilar growth reaction to recently observed positive winter-NAO phases.     

Storminess and vulnerability along the Atlantic coastlines of Europe: analysis of storm records and of a greenhouse gases induced climate scenario

Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.

An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO₂ concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO₂ concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.

The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion.     

The effect of ocean tides on a climate model simulation

We implemented an explicit forcing of the complete lunisolar tides into an ocean model which is part of a coupled atmosphere–hydrology–ocean–sea ice model. An ensemble of experiments with this climate model shows that the model is significantly affected by the induced tidal mixing and nonlinear interactions of tides with low frequency motion. The largest changes occur in the North Atlantic where the ocean current system gets changed on large scales. In particular, the pathway of the North Atlantic Current is modified resulting in improved sea surface temperature fields compared to the non-tidal run. These modifications are accompanied by a more realistic simulation of the convection in the Labrador Sea. The modification of sea surface temperature in the North Atlantic region leads to heat flux changes of up to 50 W/m². The climate simulations indicate that an improvement of the North Atlantic Current has implications for the simulation of the Western European Climate, with amplified temperature trends between 1950 and 2000, which are closer to the observed trends.     

Trans-Atlantic responses of Calanus finmarchicus populations to basin-scale forcing associated with the North Atlantic Oscillation

Populations of the copepod species Calanus finmarchicus often dominate the springtime biomass and secondary production of shelf ecosystems throughout the North Atlantic Ocean. Recently, it has been hypothesised that interannual to interdecadal fluctuations observed in such populations are driven primarily by climate-associated changes in ocean circulation. Here, we compare evidence from the North Sea and Gulf of Maine/Western Scotian Shelf (GoM/WSS) linking fluctuations in C. finmarchicus abundance to changes in ocean circulation associated with the North Atlantic Oscillation (NAO). A particularly striking contrast emerges from this Trans-Atlantic comparison: whereas the North Sea C. finmarchicus population exhibits a negative correlation with the NAO index, the GoM/WSS population exhibits a more complex, positive association with the index. The physical processes underlying these contrasting population responses are discussed in the context of regional- to basin-scale circulation changes associated with the NAO.     

On the problem of influence of the North Atlantic and Southern Oscillations on the variability of surface air temperature in the European-Mediterranean region in summer and autumn

On the basis of reanalysis of the data of the European Center of Medium-Range Weather Forecasts for 1979–1993, the interannual and monthly variability of the surface air temperature (SAT) in the European-Mediterranean region for summer and autumn with regard for the influence of the North Atlantic (NAO) and Southern (SO) Oscillations have been studied. The NAO manifests itself on a significant level from August to October and is responsible for up to 55% of the variance of monthly average SAT in the north part of the European region. This phenomenon is caused by the intensification of zonal circulation and enhanced transport of warm Atlantic air masses to Northern Europe. A general trend toward a decrease in the variance of monthly average SAT in the mature phase of the NAO is observed over the most part of Europe. In this case, the NAO is responsible for up to 35% of monthly fluctuations of SAT in summer, up to 45% in September, and up to 65% in October. As the SO index sharply decreases and an event of El Niño develops in the Pacific, the maximum variance of SAT in the European-Mediterranean region in summer significantly increases within the two-week range of variability. Up to 25% of the variance of fluctuations of SAT in summer within the indicated range of variability are, in this case, induced by the SO.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 64–70, September–October, 2004.This revised version was published online in May 2005 with corrections to cover date.     

Interdecadal changes in the links between European precipitation and atmospheric circulation during boreal spring and fall

A gridded monthly terrestrial precipitation from the Climatic Research Unit (CRU), University of East Anglia data set and the UK Met Office Northern Hemisphere mean sea level pressure data are used to investigate interdecadal changes in the relationships between precipitation variability over Europe and atmospheric circulation in the Atlantic–European sector during boreal spring and fall.
Singular value decomposition (SVD) analysis, performed for the climatic periods of strong/weak links to the North Atlantic Oscillation (NAO) during spring and fall, revealed considerable interdecadal changes both in the strength and the structure of the links between European precipitation and regional atmospheric circulation. During periods of strong links to the NAO, the leading SVD mode is characterized by the NAO-like meridional dipole in sea level pressure (SLP) fields and associated opposite precipitation variations over northern/southern Europe. When the links to the NAO are weak, the leading SVD mode is represented by the tripole pattern in SLP fields over the North Atlantic–European region, driving regional precipitation variability both in spring and fall. Further correlation analysis has shown that this mode is associated with the Scandinavian teleconnection pattern (SCA). Thus, for the considered seasons during periods of weak NAO influence, the SCA plays a role of major driver of the regional precipitation variability.     

On the mechanisms behind salinity anomaly signals of the northern North Atlantic

Hydrographic time series from the northern North Atlantic throughout the 20th century show oscillations in temperature and salinity at more or less regular intervals. The Great Salinity Anomalies described during the 1970s [Dickson, R.R., Meincke, J., Malmberg, S.-A., Lee, A.J., 1988. The “Great Salinity Anomaly” in the North Atlantic, 1968-1982. Progress in Oceanography 20, 103-151.], during the 1980s [Belkin, I.M., Levitus, S., Antonov, J., Malmberg, S.-A., 1998. “Great Salinity Anomalies” in the North Atlantic. Progress in Oceanography 41, 1-68.], and during the 1990s [Belkin, I.M., 2004. Propagation of the “Great Salinity Anomaly” of the 1990s around the northern North Atlantic. Geophysical Research Letters 31(8), L08306, doi:10.1029/2003GL019334.] have distinct amplitudes, and all three of them were interpreted as low salinity anomalies propagating downstream through the anti-clockwise circulation system of the northern North Atlantic Ocean. Further inspection of time series from the Northeast Atlantic and the Northwest Atlantic over the past century shows, however, several other distinct negative anomalies of lesser amplitudes. Additionally, a number of high salinity anomalies can be identified. The present paper analyses further the propagation of the negative and positive anomalies and links them together. It is shown that they have varying speeds of propagation, and that the varying speeds are correlated across the North Atlantic. We propose that varying volume fluxes in and out of the Arctic Basin is the causal mechanism behind the anomaly signals, and that the North Atlantic Oscillation (NAO) partly has influence on the flux variations described. Periods of large decadal-scale amplitudes of the NAO coincide with periods of large decadal-scale oscillation in the marine climate.