Time-series sediment trap record of alkenones from the western Sea of Okhotsk

C₃₇–C₃₉ alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0.1 to 5.8 μg/m²/day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be  10 °C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the U^K₃₇′ value is not significantly altered. This study indicates that U^K₃₇′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature.     

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index U^K′₃₇. Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water–sediment interface on U^K′₃₇. Alkenone sinking flux and U^K′₃₇-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the U^K′₃₇-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the U^K′₃₇-based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C_37:2 and C_38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The U^K′₃₇-based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ∼2.7–5.2% at the water–sediment interface. Despite the significant degradation of the alkenones, there was little difference in U^K′₃₇ levels between sinking particles and the surface sediment.     

Seasonal record for alkenones in sedimentary particles from the Gulf of Maine

C_37–39 alkenones and C₃₆ alkenoates, biomarkers of haptophyte origin, were measured in a 10-month sediment trap times series from the Wilkinson Basin in the Gulf of Maine (GOM). Highest biomarker flux to the seabed was observed in summertime, the period when surface waters are stratified and a persistent, subsurface chlorophyll maximum (SCM) exists within the upper thermocline and at the base of the euphotic zone throughout the GOM. Comparison of biomarker content and composition of sediment trap particles and underlying surface sediments indicates significant loss (>50%) of signal due to the impact of early diagenesis. Despite such loss, however, C₃₇ alkenone unsaturation patterns (U₃₇^K′) are not altered. Estimates of algal growth temperature made from analysis of U₃₇^K′ in these sedimentary materials correspond with water temperature measured at the SCM, identifying this biological oceanographic feature as a key site of alkenone export production to the GOM sediment record. Given the common occurrence of SCM in surface waters of the world ocean, particularly the expansive oligotrophic regions of the subtropical to temperate ocean, export of alkenones produced within such features is a potentially widespread biological oceanographic phenomenon which shapes the sediment record for these biomarkers.     

Anomalously low alkenone temperatures caused by lateral particle and sediment transport in the Malvinas Current region, western Argentine Basin

We analysed the alkenone unsaturation ratio (U^K′₃₇) in 87 surface sediment samples from the western South Atlantic (5°N–50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured U^K′₃₇ ratios were converted into temperature using the global core-top calibration of Müller et al. (1998) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by −2° to −6°C are found in the regions of the Brazil–Malvinas Confluence (35–39°S) and the Malvinas Current (41–48°S). From the oceanographic evidence these low U^K′₃₇ values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating U^K′₃₇ temperatures. In this way, particles and sediments carrying a cold water U^K′₃₇ signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.     

发展基于集合样本估计的SST张驰逼近方法用于气候模式的次表层海温场订正

An ensemble-based assimilation method is proposed for correcting the subsurface temperature field when nudging the sea surface temperature(SST) observations into the Max Planck Institute(MPI) climate model,ECHAM5/MPI-OM. This method can project SST directly to subsurface according to model ensemble-based correlations between SST and subsurface temperature. Results from a 50 year(1960–2009) assimilation experiment show the method can improve the subsurface temperature field up to 300 m compared to the qualitycontrolled subsurface ocean temperature objective analyses(EN4), through reducing the biases of the thermal states, improving the thermocline structure, and reducing the root mean square(RMS) errors. Moreover, as most of the improvements concentrate over the upper 100 m, the ocean heat content in the upper 100 m(OHT100 m)is further adopted as a property to validate the performance of the ensemble-based correction method. The results show that RMS errors of the global OHT100 m convergent to one value after several times iteration,indicating this method can represent the relationship between SST and subsurface temperature fields well, and then improve the accuracy of the simulation in the subsurface temperature of the climate model.     

Winter-to-winter recurrence of sea surface temperature, salinity and mixed layer depth anomalies

The mean seasonal cycle of mixed layer depth (MLD) in the extratropical oceans has the potential to influence temperature, salinity and mixed layer depth anomalies from one winter to the next. Temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring, and are then re-entrained into the surface layer in the subsequent fall and winter. Here we document this ‘re-emergence mechanism’ in the North Pacific Ocean using observed SSTs, subsurface temperature fields from a data assimilation system, and coupled atmosphere–ocean model simulations. Observations indicate that the dominant large-scale SST anomaly pattern that forms in the North Pacific during winter recurs in the following winter. The model simulation with mixed layer ocean physics reproduced the winter-to-winter recurrence, while model simulations with observed SSTs specified in the tropical Pacific and a 50 m slab in the North Pacific did not. This difference between the model results indicates that the winter-to-winter SST correlations are the result of the re-emergence mechanism, and not of similar atmospheric forcing of the ocean in consecutive winters. The model experiments also indicate that SST anomalies in the tropical Pacific associated with El Niño are not essential for re-emergence to occur.The recurrence of observed SST and simulated SST and SSS anomalies are found in several regions in the central North Pacific, and are quite strong in the northern (>50°N) part of the basin. The winter-to-winter autocorrelation of SSS anomalies exceed those of SST, since only the latter are strongly damped by surface fluxes. The re-emergence mechanism also has a modest influence on MLD through changes in the vertical stratification in the seasonal thermocline.     

Resuspension of benthic fluff by tidal currents in deep stratified waters, northern North Sea

Suspended particulate matter (SPM) concentration and properties (particle size and settling velocity), water column and boundary layer dynamics were measured during a 60-d period at a site in 110 m water depth in the northern North Sea. The site was in stratified waters and measurements were made during September–November as the seasonal thermocline was progressively weakening. SPM concentration was low, c. 1 mg dm⁻³ in the surface mixed layer and maximum values of 2 mg dm⁻³ in the bottom mixed layer. The bottom layer was characterised by larger mean particle size. SPM signals in the two layers were decoupled at the start of the period, when the thermocline was strong, but were increasingly coupled as the thermocline progressively weakened. A spring-neap cycle of resuspension and deposition of SPM was observed in the bottom mixed layer. Bed shear stresses were too small to entrain the bottom sediment (a fine sand) but were competent to resuspend benthic fluff: threshold bed shear stress and threshold current velocity at 10 mab were 0.02–0.03 Pa. and 0.18 m s⁻¹, respectively. Maximum SPM concentration in the bottom layer preceded peak spring tide currents by 3 d. Simulation of fluff resupension by the PROWQM model confirms that this was due to a finite supply of benthic fluff: the fluff layer was stripped from the seabed so that fluff supply was zero by the time of peak spring flow. SPM was redeposited over neap tides. Fluff resuspension must have been enhanced by intermittent inertial currents in the bottom layer but unequivocal evidence for this was not seen. There was some resuspension due to wave activity. Settling velocity spectra were unimodal or bimodal with modal values of 2×10⁻⁴–2×10⁻³ mm s⁻¹ (long-term suspension component) and 0.2–5.7 mm s⁻¹ (resuspension component). The slowest settling particles remained in suspension at peak spring tides after the fluff layer had been exhausted. There was evidence of particle disaggregation during springs and aggregation during neaps.     

Temporal and spatial variability of biogenic particles fluxes during the JGOFS northeast Atlantic process studies at 47°N, 20°W

Particle fluxes to 3100 m depth at 45°50′N, 19°30′W were measured using time-series sediment traps during a 17 month period encompassing 1989 and 1990 JGOFS spring bloom process studies in the northeast Atlantic. There was a marked intra-annual variability in fluxes of mass, particulate inorganic carbon (PIC), particulate organic carbon (POC) and opal, appearing as two major flux events in each year. In 1989, the first flux event represented the settlement of spring bloom-type material, whereas the second, in autumn, was heavily enriched in mucopolysaccharides. In 1990, in contrast, the two flux events comprised spring bloom-type material and arrived at depth at different times relative to the 1989 events. The intra- and interannual variability evident for all three biogenic components was most notable for POC: (i) the autumn 1989 event supplied twice as much POC to 3100 m as the earlier spring bloom settlement—a quite unexpected observation—and (ii) the annual average POC flux in 1989 was 3–4 times more than in 1990. A synthesis of process study datasets with sediment trap data enables an evaluation of the coupling of deep fluxes with surface-water events. Spatial variability of the 1989 deep flux events is assessed by comparing the sediment trap data reported here with those from a second site 100 km away (Honjo and Manganini,Deep-Sea Research II,40, 587–607, 1993). The timing and magnitude of the 1989 spring bloom settlement was indistinguishable in the two datasets, indicating no spatial variability in flux between these sites. In contrast, the autumn 1989 flux event was barely recorded at the second site. Given the biogeochemical importance of this latter event to deep waters, most notable in terms of its contribution to POC flux, this observation of deep-water mesoscale flux variability indicates a significant problem in determining regional carbon budgets. Construction of basin-scale budgets is a central goal of JGOFS and for this to be achieved further studies of mesoscale variability of particle flux are essential.     

Seasonal and spatial variations of zooplankton in the central and southeastern Bering Sea during the mid-1990s

Hydrographic and plankton surveys were conducted over the basin and slope of the southeastern Bering Sea during April, June/July and September of 1994 and in June/July 1995, and seasonal and spatial variations of zooplankton community were investigated in relation to the oceanographic conditions. In July 1994, sea surface temperature (SST) ranged 5.3–8.7 °C, and the thermocline was between 30 and 50 m. In July 1995, however, SST was warmer (7.3–12.4 °C), and the thermocline was shallower (20–30 m). The thermal front at the shelf was also stronger in July 1995 than in July 1994. Surface salinity was higher in 1994 than 1995. A total of 17 taxonomic groups of zooplankton were identified from the plankton samples. In 1994, the highest density was observed in September. Copepods were the major taxon during all surveys. While some taxa such as euphausiids, ostracods, and Neocalanus spp. were most abundant in spring, others such as Calanus spp., Metridia pacifica, chaetognaths, and pteropods were most abundant in September. Adults and late-stage copepodites of Eucalanus bungii were abundant in spring, and were replaced by 1st–3rd stages of copepodites in summer. Zooplankton density was ca. 4 times higher in 1995 than in 1994, in part because of warm water temperature.     

Depth habitats and seasonal distributions of recent planktic foraminifers in the Canary Islands region (29°N) based on oxygen isotopes

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ¹⁸O_shell) of five planktic foraminiferal species. Both the δ¹⁸O_shell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ¹⁸O_shell of G. ruber (w) from surface sediments is similar to the δ¹⁸O_shell values measured from the sediment-trap samples during winter. However, the δ¹⁸O_shell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ¹⁸O_shell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (～180 m) and deep surface water (～350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ¹⁸O_shell.     

Vertical transport of organic materials in the northern North Pacific as determined by sediment trap experiment

Sediment traps were deployed at 5 depths of 100 through 5,250 m to collect suspended sediments in the northern North Pacific (47°51.1'N; 176°20.6'E, 5,300 m deep) in the summer of 1978. Fatty acid composition was determined in the samples of phytoplankton, particulate matter, trap sediment and bottom sediment.Fatty acid composition of the trap sediments revealed no significant vertical trend throughout the water column from depths of 100 to 5,250 m, and were also similar to those of the phytoplankton and the particulate matter from the euphotic layer. However, a marked difference in the fatty acid composition was observed between the trap sediments and the particulate matter from deep waters. Therefore, it can be concluded that the source of fatty acids in the trap sediments is the particulate matter from the euphotic layer but not from deep waters.Unsaturated fatty acids highly susceptible to biological agents were rather abundant in the trap sediments as well as in the phytoplankton and particulate matter from the euphotic layer, however no unsaturated fatty acid was found in the particulate matter from deep waters. From these findings, it is clear that the particulate matter of the euphotic layer is transported to deep waters very rapidly. As the sinking rate of fecal pellets produced by zooplankton is in the range of ten to hundreds of meters a day, fecal pellets are assumed to be the most likely carrier of rapid-transport of organic matter including fatty acids from the euphotic layer to deep waters.     

Seasonal and interannual variability of the planktic foraminiferal flux in the vicinity of the Azores Current

Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.     

Particulate flux in the water column overlying Santa Monica Basin

Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45 μm silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data, but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone.Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m⁻²d⁻¹ at 110–135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835–860m) were 50, 6.5, 0.64, 41.6 and 575mg m⁻²d⁻¹ for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone. The latter agree with rates previously inferred from the sedimentary record using ²¹⁰Pb as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent with the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method.     

三门湾沉积记录中长链烯酮不饱和指数-海表温度和浮游动物群落对厄尔尼诺/拉尼娜的响应

应用沉积地层记录中长链烯酮不饱和指数(U3K7)估算1916—2003年三门湾表层海水温度(SST)与变化。SST波动范围为15.97~18.00℃,年平均为17.03℃。该值比当年实测海水全年平均温度低3.52℃,同时应用长链烯醇不饱和指数与SST的关系重建历史上的厄尔尼诺现象。研究显示三门湾的厄尔尼诺气候事件在大尺度上与东太平洋一样均受制于气候影响,在变化尺度上又受到地理位置和地方性气候(季风)的影响,厄尔尼诺事件在形式和年代上相互对应,但是其涛动幅度不如东太平洋的强烈。通过比较厄尔尼诺期间(2003/2002年)和非厄尔尼诺期间(2006/2005年)的浮游动物群落结构变动信号、生物量、密度以及物种多样性等,在厄尔尼诺时期浮游动物种类数、生物量和丰度呈现偏高的趋势,三门湾的暖水性浮游动物类群、数量变化与台湾暖流活动过程中携带的浮游性动物有密切的联系。     

沉积物捕获器在海岸与陆架沉积动力研究中的应用:以罗源湾和台湾海峡为例

运用时间序列的沉积物捕获器对海岸与陆架海域沉降颗粒物进行采集,估算沉降通量,并运用多学科综合研究手段分析沉降颗粒物的来源、组成、时空变化及控制因素,可以为海岸与陆架沉积动力过程的研究提供新的研究手段。福建罗源湾的实验表明,夏季罗源湾潮下带小潮至中潮期间的沉降通量为133.20~256.18g/(m2·t);由中潮向大潮变化期间单个潮周期的沉降通量明显增大,台风过后的大潮期间的沉降通量为373.99~590.51g/(m2·t);台风显著影响期间的沉降通量为746.34g/(m2·t);粒度分析及水动力观测结果显示,观测期间罗源湾潮下带沉降颗粒物主要来源于海底沉积物的再悬浮。台湾海峡西北部内陆架海域的实验研究表明,该海域近底部悬浮颗粒物沉降通量最大值为13.34g/(m2·d),由小潮向中潮沉降通量逐渐增大,这主要是由于近底部温盐跃层层位上移,近底部垂向混合作用增强,致使底部再悬浮沉积物向上扩散,并最终被沉积物捕获器捕获。沉积物捕获器可以接收到再悬浮沉积物,结合底部边界层过程的观测研究,可以深入认识海底沉积物的侵蚀、沉降及埋藏过程,在研究海岸与陆架区沉积动力学、泥质区沉积记录的形成过程与保存潜力中扮演着十分重要的角色。     

Ocean variability North of New Guinea derived from TRITON buoy data

We investigated variability in the ocean surface-subsurface layer north of New Guinea using Triangle Trans-Ocean Buoy Network (TRITON) buoys at 2°N, 138°E and 0°N, 138°E during the period from October 1999 to July 2004. Both North and South Pacific waters were observed below the subsurface at these stations. The variability in the subsurface waters was particularly high at 2°N, 138°E. Clear interannual variability occurred near the surface; the water type differed before and after onset of the 2002–03 El Niño. Before summer 2001, water that appeared to be advected from the central equatorial Pacific occupied the near surface layer. After autumn 2001, waters advected by the New Guinea Coastal Current were observed near the surface. Intraseasonal and seasonal variations were also observed below the subsurface. With regard to seasonal variability, the salinity of the subsurface saline water, the South Pacific Tropical Water, was generally high during the boreal summer-autumn, when the New Guinea Coastal Undercurrent was strong. Intraseasonal fluctuations on a scale of 20 to 60 days were also seen and may have been associated with intrinsic oceanic variability, such as ocean eddies, near the stations. Ocean variability in the thermocline layer between 100 and 200 m greatly affects the surface dynamic height variability; water variability before 2001 and variability in the pycnocline depth after 2002 are important factors affecting the thermocline.     

Internal recycling of particle reactive organic chemicals in the Chesapeake Bay water column

Hydrophobic organic contaminants (HOCs) may be used as tracers of particle dynamics in aquatic systems. Internal cycling of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were studied in the mesohaline Chesapeake Bay to assess the role of resuspension in maintaining particle and contaminant inventories in the water column, and to compare settling and suspended particle characteristics. Direct measurements of sediment resuspension and settling conducted in conjunction with one of the sediment trap deployments indicate reasonable agreement between measurements of particle flux using the two different methods. Organic carbon and PCB concentrations in settling solids collected in near-surface sediment traps were remarkably lower than concentrations in suspended particles collected by filtration during the trap deployments, but higher PAH concentrations were found in the settling particles. The different behaviors of PAHs and PCBs in the settling particles are due to their different source types and association to different types of particles. Sediment trap collections in near bottom waters were dominated by resuspension. Resuspension fluxes of HOCs measured 2 m above the bay bottom were as high as 2.5 μg/m² day for total PCBs and 15 μg/m² day for fluoranthene, and were 25 and 10 times higher than their settling fluxes from surface waters, respectively. HOC concentrations in the near bottom traps varied much less between trap deployments than HOC concentrations in the surface traps, indicating that the chemical composition of the resuspended particles collected in the near bottom traps was more time-averaged by repeated resuspension than the surface particles.     

Interdecadal climate regime dynamics in the North Pacific Ocean: theories, observations and ecosystem impacts

Basin-scale variations in oceanic physical variables are thought to organize patterns of biological response across the Pacific Ocean over decadal time scales. Different physical mechanisms can be responsible for the diverse basin-scale patterns of sea-surface temperature (SST), mixed-layer depth, thermocline depth, and horizontal currents, although they are linked in various ways. In light of various theories and observations, we interpret observed basinwide patterns of decadal-scale variations in upper-ocean temperatures. Evidence so far indicates that large-scale perturbations of the Aleutian Low generate temperature anomalies in the central and eastern North Pacific through the combined action of net surface heat flux, turbulent mixing and Ekman advection. The surface-forced temperature anomalies in the central North Pacific subduct and propagate southwestwards in the ocean thermocline to the subtropics but apparently do not reach the equator. The large-scale Ekman pumping resulting from changes of the Aleutian Low forces western-intensified thermocline depth anomalies that are approximately consistent with Sverdrup theory. These thermocline changes are associated with SST anomalies in the Kuroshio/Oyashio Extension that are of the same sign as those in the central North Pacific, but lagged by several years. The physics of the possible feedback from the SST anomalies to the Aleutian Low, which might close a coupled ocean–atmosphere mode of decadal variability, is poorly understood and is an area of active research. The possible responses of North Pacific Ocean ecosystems to these complicated physical patterns is summarized.     

Seasonality of foraminiferal flux in sediment traps at Chatham Rise,SW Pacific: implications for paleotemperature estimates

Analysis of sediment traps located either side of the Subtropical Front east of New Zealand reveals a strong association between water masses and foraminiferal assemblages. The composition and timing of foraminiferal productivity is distinct between waters north and south of the front, and these differences are also reflected in the assemblages of nearby core-tops. The sediment trap data indicate highly seasonal flux patterns in this region, so sedimentary records may represent flux during a particular season, rather than throughout the annual cycle. This pronounced seasonality has implications for our estimates of the annual temperature range based on faunal assemblages. This study shows that despite strong flux seasonality the annual sea-surface temperature (SST) range is reliably estimated from the sediment trap foraminiferal assemblages by the modern analog technique. The successful estimation of the annual SST range also indicates that the annual flux obtained from these sediment traps is representative of the longer term flux preserved in surface sediments. Core-top assemblages from this region can therefore be directly related to modern sea-surface conditions, providing an analogue for interpreting past environmental change from fossil assemblages.