Basin geometry and salt diapirs in the Flinders Ranges,South Australia: Insights gained from geologically-constrained modelling of potential field data

The Adelaide Basin in Australia is a complex of late Neoproterozoic to Early Cambrian rift and sag basins which was inverted during the Cambro–Ordovician Delamerian Orogeny. The deposition of evaporitic sediments during the earliest stage of basin development in the late Neoproterozoic (Willouran age) played a major role in the subsequent tectonic evolution of the basin. Previous studies have shown that early mobilization, vertical transport and withdrawal of the evaporites influenced the sedimentation during the late Neoproterozoic and Early Cambrian. The evaporites also influenced deformation during the inversion of the basin and the development of the Delamerian fold and thrust belt. However, the control exerted by basement structures in the deposition of the evaporitic beds and the role of these tectonic structures in the later inversion of the basin have been poorly constrained.     

TEM investigations of South Atlantic Ridge 13.2°S hydrothermal area

According to the exploration contract about polymetallic sulfides in the SWIR （Southwest Indian Ridge） signed by China with the International Seabed Authority, to delineate sulfide minerals and estimate resource quantity are urgent tasks. We independently developed our first coincident loop Transient Electromagnetic Method （TEM） device in 2010, and gained the TEM data for seafloor sulfide at South Atlantic Ridge 13.2°S in June 2011. In contrast with the widely applied CSEM （Marine controlled-source electromagnetic） method, whose goal is to explore hydrocarbons （oil/gas） of higher resistivity than seawater from 102 to 103 m below the sea floor, the TEM is for low resistivity minerals, and the target depth is from 0 to 100 m below the sea floor. Based on the development of complex sulfide geoelectrial models, this paper analyzed the TEM data obtained, proposing a new method for seafloor sulfide detection. We present the preliminary trial results, in the form of apparent resistivity sections for both half-space and full-space conditions. The results cor- respond well with the observations of the actual hydrothermal vent area, and the detection depth reached 50-100m below the bed, which verified the capability of the equipment.     

南大西洋副热带偶极子的年际变化

南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。     

Segmentation and volcano-tectonic characteristics along the SW African continental margin,South Atlantic,as derived from multichannel seismic and potential field data

Regional seismic reflection and potential field data document the South Atlantic's break-up history, between 39°S and 19°S, from the Early Cretaceous onwards. Previous maps of distribution of volcanics along the margin showed volcanics along the whole African margin based on extrapolation of data. Based on previously unpublished marine geophysical data, we found the southernmost 460 km long margin segment to be lacking huge volumes of break-up related volcanic effusives. Northwards, break-up was accompanied by the emplacement of huge volumes of volcanic material, prominently featured in seismic sections as huge wedge-shaped seaward dipping reflectors (SDRs). Detailed mapping of offsets (left- and right-stepping) and variations in structural character of the volcanics reveal the segmentation along and the break-up history of the margin. Several superimposed SDR sequences, suggesting episodicity of volcanic emplacement (divided by periods of erosion and sedimentation), are distinct along southerly lines, losing prominence northwards.A main outcome of our study is that this passive margin is not continuously of the volcanic type and that the change from a non-volcanic to a volcanic margin occurs abruptly.We define four distinct First-order Segments along the 2400 km section of the southwestern African margin covered by our seismic data. From south to north these First-order Segments are: Magma-poor Segment I; Segment II with enormous SDRs volumes; decreasing SDRs volumes in Segment III; Segment IV again with enormous volcanic output, likely influenced by Walvis Ridge volcanism.Most important is that there is no systematic increase in the volumes of the effusives towards the Tristan da Cunha hot-spot. Rather there is an alternating pattern in the SDRs' volumes and widths.The boundary between the volcanic and magma-poor margin segments in the southernmost study area is sharp (10s of km), which we propose is reflected in magnetic anomaly data as well. We suggest that this variability along the margin is mainly due to a change in stretching/rifting character from oblique during the early stages of breakup to conventional seafloor spreading from Chron M4 (∼130 Ma) onwards.     

A Zonal Pathway for NADW in the South Atlantic

Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers.     

热带大西洋对全球变暖的响应

与太平洋和印度洋不同，全球变暖下热带大西洋变化的研究较少。本文使用地球系统模型CESM（Community Earth System Model），发现全球变暖后热带大西洋在秋季的升温类似大西洋尼诺（Atlantic Niño）的正位相，即大西洋西部增暖幅度小于东部；在夏季类似大西洋尼诺的负位相，即大西洋西部增暖幅度大于东部。利用覆盖（overriding）技术，分离了风应力、风速和CO₂的直接热效应对海洋升温的作用，探讨了大西洋尼诺本身和全球变暖作用下类似大西洋尼诺正位相（下文简称“类大西洋尼诺升温”）的形成机制。结果表明，这两种情况下的形成机制基本相同，风应力的变化是导致大西洋东部暖异常的主要机制。但两者之间也存在区别：1）全球变暖下海表温度的季节变化振幅减小，而大西洋尼诺时变化不大；2）全球变暖下西风异常主要集中在大西洋东部，而大西洋尼诺时主要集中在大西洋中部；3）除风应力外，CO₂的热效应对类尼诺升温的变化也有一定影响。     

Stress field modeling of northwestern South China Sea since 5.3 Ma and its tectonic significance

Tectonically, the northwestern South China Sea （SCS） is located at the junction between three micro-plates, i.e., the Indochina, South China and Zhongsha-Xisha micro-plates, and involves three basins, i.e., the Yinggehai Basin, the Qiongdongnan Basin and Xisha Trough in the east, and the Zhongjiannan Basin in the south. Since the Pliocene （5.3 Ma）, the Yinggehai Basin has experienced repeated accelerating subsidence, high thermal fluid, and widely developing mud-rich overpressure chambers, abundant mud diapers and crust-mantle mixed CO2. While a large central canyon was developed in the Qiongdongnan Basin, new rift occurred in the Xisha ~rough. These characteristics demonstrate a single tectonic unit for the northwestern SCS, for which we have undertaken stress field modeling to understand its plate deformations and sedimen- tary responses. Our results demonstrate that an extension tectonic event occurred after 5.3 Ma in theYingge- hal-Qiongdongnan-Xisha trough area, which is characterized by thinner crust C〈16000 m）, half-graben or graben structural style and thicker sedimentary sequences （〉3 500 m）. A new rift system subsequently was developed in this area; this event was mainly driven by the combined effects of different movement veloc- ity and direction of the three micro-plates, and the far-field effect of the continental collision between the Indian Plate and the Tibetan Plateau, and subduction of the Pacific Plate underneath the Eurasian Plate.     

Submarine groundwater discharge: A large, previously unrecognized source of dissolved iron to the South Atlantic Ocean

This paper reports the initial results of a study of groundwater and coastal waters of southern Brazil adjacent to a 240 km barrier spit separating the Patos Lagoon, the largest coastal lagoon in South America, from the South Atlantic Ocean. The objective of this research is to assess the chemical alteration of freshwater and freshwater–seawater mixtures advecting through coastal permeable sands, and the influence of the submarine discharge of these fluids (SGD) on the chemistry of coastal waters. Here we focus on dissolved iron in this system and use radium isotopic tracers to quantify SGD and cross-shelf fluxes. Iron concentrations in groundwaters vary between 0.6 and 180 μM. The influence of the submarine discharge of these fluids into the surf zone produces dissolved Fe concentrations as high as several micromolar in coastal surface waters. The offshore gradient of dissolved Fe, coupled with results for Ra isotopes, is used to quantify the SGD flux of dissolved Fe from this coastline. We estimate the SGD flux to be 2 × 10⁶ mol day^− 1 and the cross-shelf flux to be 3.2 × 10⁵ mol day^− 1. This latter flux is equal to about 10% of the soluble atmospheric Fe flux to the entire South Atlantic Ocean. We speculate on the importance of this previously unrecognized iron input to regional ocean production and on the potential significance of this source to understanding variations in glacial–interglacial ocean production.     

Tectonics, global changes in sea level and their relationship to stratigraphical sequences at the US Atlantic continental margin

The principal factors that control the extent of seas through geological time are vertical movements of the lithosphere and global changes in sea level. The relative height of the sea surface determines the facies and the thickness of sediments that can accumulate in a sedimentary basin. Backstripping studies show that the primary factors affecting the subsidence of rifted sedimentary basins are thermal contraction, following heating and thinning of the lithosphere at the time of rifting, and sedimentary loading. Factors such as compaction, palaeobathymetry, erosion and global sea level changes also contribute, but their combined affects are small compared to those of thermal contraction and sedimentary loading. Simple models have been constructed which combine the effects of sedimentary loading and thermal contraction with those of compaction, sub-aerial erosion and global changes in sea level. In the models it was assumed that the lithosphere was heated and thinned by stretching at the time of rifting, sedimentary loading occurs by flexure of a lithosphere that progressively increases its flexural rigidity with age following rifting and, that sediment compaction and bathymetry change across a basin but do not vary significantly with gwological time. Furthermore, different assumptions were made on the magnitude of curves of global sea level changes and the relationship between denudation rate and regional elevation. The models show that tectonics, in the form of thermal contraction of the lithosphere and flexure and slowly varying global changes in sea level, can explain a number of the stratigraphic features of the US Atlantic continental margin. In this Paper some of the implications of these results are examined for studies of (a) sea level changes through geological time; and (b) the maturation history of continental margin basins.     

南大西洋热液沉积物的不同相态提取方法与元素赋存状态

本文对采自南大西洋受不同程度热液活动影响的表层沉积物样品进行了元素和矿物组成分析,并对热液沉积物的碳酸盐相、Fe-Mn氧化物相和残渣态进行了一系列顺序提取实验。选用不同浓度的盐酸羟胺(HH)和醋酸(HAc)混合溶液对样品的Fe-Mn氧化物相进行提取,通过分析不同实验条件下Fe-Mn氧化物相Ti/Nd、Ti/Pb比值和Fe-Mn氧化物相、残渣态的稀土元素(REE)标准化配分模式及Ce和Eu异常值,确定了不同类型热液沉积物样品Fe-Mn氧化物相提取的理想试剂条件均为0.5 mol/L HH和25% HAc混合溶液。研究结果表明,受热液活动影响程度越高,沉积物中Fe、Cu、Zn等元素含量越高,Ca、Sr、Ba含量呈相反趋势,Mn、Pb和REE未受到热液活动明显影响;随着受热液活动影响增强,Ca、Sr、Nd在Fe-Mn氧化物相中所占比例增加,在残渣态中降低,Mn、Co、Ni和Zn呈相反趋势,Cu在碳酸盐相所占比例增加,在残渣态中降低,Pb赋存状态不受热液活动影响,主要赋存于Fe-Mn氧化物相;REE主要赋存于残渣态,沉积物受热液活动影响越明显,残留相对REE富集能力越强,残渣态REE球粒陨石标准化配分模式表现为LREE相对富集越来越不明显的特征。本文研究为进一步了解南大西洋热液沉积物特征和热液活动对沉积物元素赋存状态影响提供了方法和地球化学数据支持。     

南大西洋两岸盆地海相烃源岩特征与控制因素

南大西洋两岸盆地漂移期层系油气资源十分丰富,通过对两岸重点盆地漂移期主力烃源岩发育层位、生烃潜力、识别特征和分布范围对比分析,明确两岸发育早、晚两套主力海相烃源岩。其中,晚期的赛诺曼—土仑阶海相烃源岩分布范围较广。整体上,两岸北段和赤道段盆地漂移期主力烃源岩地化指标优于中段和南段盆地,西非一侧海域盆地烃源岩地化指标优于南美一侧盆地。在对重点钻井的矿物元素化验分析、沉积相和古地理分析基础之上,总结了局限海湾的古地理背景和沉积相带类型控制优质海相烃源岩发育程度和分布范围的规律,并进一步指出南大西洋两岸北段和赤道段盆地漂移期成熟生烃灶平面分布范围内的深水沉积砂体是主要有利勘探方向,以找油为主,中段含盐盆地内紧邻盐微盆的漂移期深水沉积砂体勘探潜力次之。     

Ocean circulation patterns and dust supply into the South Atlantic during the last glacial cycle revealed by statistical analysis of kaolinite/chlorite ratios

Multivariate statistical analysis on the kaolinite/chlorite ratios from 20 South Atlantic sediment cores allowed for the extraction of two processes controlling the fluctuations of the kaolinite/chlorite ratio during the last 130,000 yrs, (1) the relative strength of North Atlantic Deep Water (NADW) inflow into the South Atlantic Ocean and (2) the influx of aeolian sediments from the south African continent. The NADW fluctuation can be traced in the entire deep South Atlantic while the dust signal is restricted to the vicinity of South Africa. Our data indicate that NADW formation underwent significant changes in response to glacial/interglacial climate changes with enhanced export to the Southern Hemisphere during interglacials. The most pronounced phases with Enhanced South African Dust Export (ESADE) occurred during cold Marine Isotope Stage (MIS) 5d and across the Late Glacial/Holocene transition from 16 ka to 4 ka (MIS 2 to 1). This particular pattern is attributed to the interaction of Antarctic Sea Ice extent, the position of the westerlies and the South African monsoon system.     

The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

The Agulhas Ridge is a prominent topographic feature that parallels the Agulhas-Falkland Fracture Zone (AFFZ). Seismic reflection and wide angle/refraction data have led to the classification of this feature as a transverse ridge. Changes in spreading rate and direction associated with ridge jumps, combined with asymmetric spreading within the Agulhas Basin, modified the stress field across the fracture zone. Moreover, passing the Agulhas Ridge’s location between 80 and 69 Ma, the Bouvet and Shona Hotspots may have supplied excess material to this part of the AFFZ thus altering the ridge’s structure. The low crustal velocities and overthickened crust of the northern Agulhas Ridge segment indicate a possible continental affinity that suggests it may be formed by a small continental sliver, which was severed off the Maurice Ewing Bank during the opening of the South Atlantic. In early Oligocene times the Agulhas Ridge was tectono-magmatically reactivated, as documented by the presence of basement highs disturbing and disrupting the sedimentary column in the Cape Basin. We consider the Discovery Hotspot, which distributes plume material southwards across the AAFZ, as a source for the magmatic material.     

Cyclic fluctuations of anoxia during Cretaceous time in the South Atlantic Ocean

The holes of the DSDP-IPOD program in the South Atlantic Ocean document two major anoxic events during Oxfordian to middle Albian times and secondly from late Cenomanian to Santonian times. The black shales formed during these two anoxic events differ in their rhythmicity and origin.During Lower Cretaceous time, the anoxic conditions resulted from the confined, euxinic nature of the basins. The rhythmicity of these black shales probably does not result from a global phenomenon (climatic or tectono-eustatic), but from local conditions resulting from the slender dimensions of the young ocean basin(s). The diversity and the diachroneity of the deposits from the south to the north precisely reflect the dynamics of the oceanic spreading.During Upper Cretaceous time, the anoxic conditions fluctuated in relation to a mid-water oxygen-minimum zone. The rhythmicity of black shale deposition seems to result from a global phenomenon, because of the widespread occurrence of the event. In the South Atlantic ocean, the cyclic fluctuations of anoxia were due to cyclic variations in the depth of the mid-water oxygen-minimum zone. There is no simple process to explain such rhythmicity. It probably results from the interplay of the three main variables which characterize the oceans at the time of the Cenomanian-Turonian boundary: the increased rate of sea floor spreading, high sea-levels and low water-circulation.     

Tectonic control of the oil-rich large igneous-carbonate-salt province of the South Atlantic rift

The Early Cretaceous South Atlantic Magmatic Province (SAMP), which includes the Paraná-Etendeka LIP, produced about 8 million km³ of tholeiitic basalt and diabase over an area of 4 million km². Huge pre-salt oil reserves, discovered in 2007 by Petrobras in non-marine carbonates, are estimated at more than 45 billion barrels. Here we show the close causal relationship of the southward increasing width of the wedge-shaped South Atlantic rift with the similarly southward increase in igneous activity, in the thicknesses of non-marine carbonate and salt, and in the size of oil reserves, all controlled mainly by South America’s early clockwise rotation away from Africa about a pole in its northeast. Large diabase dike swarms transversal to the rift witness to South America’s rotation that opened in its wake the southward widening South Atlantic rift. Westward increasing pressure on the Equatorial margin by South America’s clockwise rotation forced open the Benue trough and created pre-late-Aptian folds in the Demerara Plateau and in Brazil’s Solimões (Upper Amazonas) basin. Prerift and synrift volcanic activity increases southward, culminating in the Parana-Etendeka LIP and in the offshore volcanic SDRSs that continue southward to the Cape Basin. Berriasian-Valanginian rift sediments deposited from about 145 Ma, 10 Ma before the flood basalts of the Parana-Etendeka LIP. The largest transversal dike swarm continued in the proto-Walvis Ridge that separated the central South Atlantic endorheic rift basin from the sea in the south; erosion and leaching of basalts supplied Ca, Mg, and SiO₂ to the endorheic basin for the deposition of non-marine carbonates and authigenic clays. Basalt flows intercalated with carbonates nearly until salt deposition about 113 Ma. Hypogenic leaching of carbonates by mantle-derived CO₂ created optimal reservoirs. Supergiant oil deposits occur where the widest endorheic basin and the volcanic province overlap.     

Origin of “paired” aseismic rises: Ceará and Sierra Leone rises in the equatorial, and the Rio Grande Rise and Walvis Ridge in the South Atlantic

In the equatorial Atlantic the Ceará and Sierra Leone rises lie on opposing sides of the mid-ocean ridge and are equidistant from its axis. The northern and southern boundaries respectively, of the two rises are formed by the same fracture zones. The area of shallowest acoustic basement under the Ceará Rise coincides with the presence of a 1–2 km thick seismic layer (velocity: 3.5 km/sec) lying over the oceanic layer 2. This 3.5 km/sec layer is interpreted as a sequence of volcanics which began erupting about 80 m.y. ago when the sites of the two rises lay at the ridge axis. As the “abnormal” volcanic activity ceased, the breakup of this volcanic pile into two pieces has formed the Ceará and Sierra Leone rises.

In the South Atlantic, the northern and southern boundaries of the Rio Grande Rise are also formed by fracture zones and an approximately 1 km thick layer with a velocity of 3.5 km/sec exists also under this rise. The same fracture zones appear to bound the Walvis Ridge. Drilling data suggests that both the Rio Grande Rise and Walvis Ridge have subsided continuously since their creation. The igneous rocks recovered from both rises consist of alkalic basaltic suites typical of oceanic volcanic islands. The existing data favor a model in which “excessive” volcanism along the same segment of the Mid-Atlantic Ridge created both the South Atlantic aseismic rises between 100 and 80 m.y. ago. In both the examples, the northern and southern boundaries of the rises are formed by the same fracture zones which originally bounded the abnormally active segment of the ridge axis.     

Characterization of dissolved organic matter fluorescence in the South Atlantic Bight with use of PARAFAC model: Interannual variability

Systematic water sampling for characterization of chromophoric dissolved organic matter (CDOM) in the coastal South Atlantic Bight, was conducted as part of the long term Coastal Ocean Research and Monitoring Program (CORMP). Water samples were collected during a 3.5 year period, from October 2001 until March 2005, in the vicinity of the Cape Fear River (CFR) outlet and in adjacent Onslow Bay (OB). During this study there were two divergent hydrological and meteorological conditions in the CFR drainage area: a severe drought in 2002, followed by the very wet year of 2003. CDOM was characterized optically by the absorption coefficient at 350 nm, the spectral slope coefficient (S), and by Excitation Emission Matrix (EEM) fluorescence. Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra and six components were identified: three terrestrial humic-like components, one marine humic-like component and two protein-like components. Terrestrial humic-like components contributed most to dissolved organic matter (DOM) fluorescence in the low salinity plume of the CFR. The contribution of terrestrial humic-like components to DOM fluorescence in OB was much smaller than in the CFR plume area. Protein-like components contributed significantly to DOM fluorescence in the coastal ocean of OB and they dominated DOM fluorescence in the Gulf Stream waters. Hydrological conditions during the observation period significantly impacted both concentration and composition of CDOM found in the estuary and coastal ocean. In the CFR plume, there was an order of magnitude difference in CDOM absorption and fluorescence intensity between samples collected during the drought compared to the wet period. During the drought, CDOM in the CFR plume was composed of equal proportions of terrestrial humic-like components (ca. 60% of the total fluorescence intensity) with a significant contribution of proteinaceous substances (ca. 20% of the total fluorescence). During high river flow, CDOM was composed mostly of humic substances (nearly 75% of total fluorescence) with minor contributions by proteinaceous substances. The impact of changes in fresh water discharge patterns on CDOM concentration and composition was also observed in OB, though to a lesser degree.     

Basin-scale distributions of stable nitrogen isotopes in the subtropical North Atlantic Ocean: Contribution of diazotroph nitrogen to particulate organic matter and mesozooplankton

New N inputs via biological N₂-fixation play a critical role in supporting oceanic primary production and influencing global biogeochemical cycles. Numerous studies have documented significant N₂-fixation rates in the North Atlantic, but relatively little is known of the pathways and fluxes of new N through planktonic food webs. Here, we report the natural abundance of ¹⁵N in, and contribution of diazotroph N (N_D) inputs to, suspended particles and mesozooplankton collected along two transects in the subtropical North Atlantic Ocean (STNA). Samples were collected in April-May 2000 along the two main transects to evaluate spatial trends of ¹⁵N within the Western Atlantic and across the basin. We found that N₂-fixation is a key component in supporting both primary and secondary productions throughout the STNA. N_D contribution was generally higher for suspended particles than for mesozooplankton, and we observed a high N_D contribution to suspended particles over large spatial scales in the western and central STNA. Mesozooplankton N_D incorporation suggests that diazotroph production supports oceanic food webs over longer timescales (e.g., weeks to months) than that of particle turnover (e.g., days). Larger mesozooplankton (1000-4000 ??m) generally incorporated more N_D than smaller mesozooplankton (250-1000 ??m), and thus may exert a stronger influence on an N_D movement within the water column. Spatial and vertical patterns of variation in mesozooplankton ??¹⁵N also suggest either broad geographical differences in an N_D contribution to secondary production, or temporal variations in N_D incorporation via mesozooplankton communities.     

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.