On the size of the Peru upwelling ecosystem

Previously published estimates of the area of the Peru upwelling ecosystem vary by more than an order of magnitude. In an effort to improve this situation, we used a 24-month sequence of SeaWiFS satellite images of chlorophyll in the surface water off Peru from 5°S to 18.5°S during September 1997–August 1999 to estimate the size of the nutrient enhanced productive habitat associated with the upwelling. The first 12-month period was marked by El Niño conditions, the second by strong upwelling. Using a chlorophyll threshold of >1.0 mg m⁻³ to define the limit of the productive habitat resulted in maximum area estimates of 120×10³ km² during September 1997–August 1998, and 220×10³ km² during September 1998–August 1999. The latter result is consistent with an area estimate we calculated using total fishery landings and a regression relating fishery yields per unit area to annual primary production per unit area. Although year-to-year variation in the annual mean size of the upwelling ecosystem must be significant, even discounting El Niño events, our analysis has shown that at least five of the extreme earlier values are not good estimates of the size of the productive habitat. We may now be close to knowing the average size of the ecosystem to within a factor of about two.     

Iron,macronutrients and diatom blooms in the Peru upwelling regime: brown and blue waters of Peru

Surface water transects and vertical profiles for dissolved iron, macronutrients, chlorophyll a (Chl a), and hydrographic data were obtained in the Peru upwelling regime during August and September 2000. The supply of the micronutrient iron, relative to that of the macronutrients nitrate, phosphate and silicic acid, is shown to play a critical role in allowing extensive diatom blooms to develop in the Peru upwelling system. The extremely high-chlorophyll “brown waters of Peru” (with Chl a concentrations between 20 and 45 μg/l) result from massive diatom blooms with maximal photochemical efficiencies (F_v/F_m >0.6) occurring in the iron-rich upwelling region observed over the broad continental shelf off northern and central Peru. The source of the upwelled water in this region is the nutrient-rich subsurface countercurrent in contact with the organic-rich shelf sediments. This subsurface shelf water is suboxic and has extremely high concentrations of dissolved Fe (>50 nM) in the near-bottom waters. In marked contrast, relatively low-chlorophyll “blue waters” (Chl a <2 μg/l) with low concentrations of dissolved Fe (<0.1 nM) and high unutilized macronutrient concentrations are observed in the coastal upwelled waters along the southern coast of Peru and in the offshore regions of the Peru Current. Southern Peru is a region without a wide shelf to serve as a source of iron and, as a result, dissolved Fe concentrations in the near-bottom suboxic waters of this region are an order-of-magnitude lower than observed off northern and central Peru. In addition, the offshore Peru Current is a broad, Fe-limited, high-nitrate, lower than expected chlorophyll region extending hundreds of kilometers offshore into the northeast region of the South Pacific subtropical gyre and northwestward into the South Equatorial Pacific.     

Wax esters and triacylglycerols in sinking particulate matter in the Peru upwelling area (15°S, 75°W)

The flux and composition of wax esters and triacylglycerols were measured in particulate matter collected by free-drifting sediment traps in the Peru upwelling area. The purpose was to assess diurnal variations in sources and vertical transport of these lipids. Traps were deployed for periods of 8–12 h during both day and night at the base of the euphotic zone (10–14m) and at about 50m. Although the flux of total particulate organic carbon varied 4×, the flux of wax esters varied by 84× and triacylglycerols by 30×. POC, wax esters, and triacylglycerols also showed different temporal patterns. The highest wax ester flux was measured in shallow traps at night and is attributed to increased inputs from zooplankton which feed near the surface at night. Triacylglycerol flux was high in both shallow and deep nocturnal traps, consistent with inputs of both phytoplankton and zooplankton lipids. The composition of these lipids was also quite variable and attests to the complex nature of the lipid sources.     

Phytoplankton assemblages in the CoOP-WEST coastal upwelling area

Elevated levels of phytoplankton were observed at the Northern California coastal upwelling ecosystem studied as part of the CoOP-WEST project during monthly summer surveys in 2000, 2001 and 2002. The high concentrations of chlorophyll were made up mostly of larger cells; the phytoplankton communities that resulted were dominated by centric diatoms. The highest chlorophyll a concentrations were observed when large diatoms or small colony-forming species dominated the assemblages. In contrast, when smaller nano-flagellates and picoplankton were dominant, total chlorophyll a concentrations were over four or five-fold lower than when diatoms were prevalent, illustrating the importance of large diatoms to total phytoplankton biomass. Each year, when chlorophyll concentrations were greatest, Chaetoceros species created a Chaetoceros-dominated system. A few other genera contributed to the upwelling diatom community, mostly the centric diatoms Asterionella, Thalassiosira, Rhizosolenia (including Guinardia and Proboscia), and the pennate Nitzschia. These diatoms have been described in other coastal upwelling ecosystems, and at this study site form a functional group that are apparently well adapted to the high-nutrient, turbulent conditions that are typical of these coastal regions.     

Pleistocene surface water temperatures in the Benguela upwelling area

Analysis of carbonate microfossils (planktonic foraminifers and nannoplankton) in the DSDP Hole 362 Quaternary section made it possible to specify its zonal subdivision (almost all zones of Gartner’s high-resolution nannofossil scale are recognized), establish depositional environments, and restore past surface water temperatures. The latter appeared to be several degrees lower than their present-day values, which is evident from the anomalously high share of the subpolar species Neogloboquadrina pachyderma sin. that constitutes 97% of the fossil assemblage in Lower Pleistocene sediments. It is shown that the Benguela upwelling existed throughout the entire Pleistocene, being less intense in the Late Pleistocene and Holocene.     

Nepheloid layer distribution in the Benguela upwelling area offshore Namibia

The distribution of nepheloid layers across the outer shelf and upper continental slope off Namibia was studied during a cruise with R.V. Meteor in late austral summer 2003. Optical measurements, carried out with a transmissometer and a backscattering fluorometer, are correlated with suspended particulate matter (SPM) and particulate organic carbon (POC) values from water sample filtration. Conductivity-temperature-depth and oxygen data are used to relate the nepheloid layers to hydrographic structures. The particle content of surface water at the continental slope is controlled primarily by the offshore extension of highly productive upwelling filaments. A pronounced bottom nepheloid layer (BNL) covers the entire area of study with maximum intensity above the outer shelf and at the shelf break—an area where erosional forces dominate. The detachment of this BNL at the shelf break feeds a major intermediate nepheloid layer (INL) at 25.5°S. This INL is positioned at 250–400 m depth, at the lower boundary of an oxygen minimum zone, and is likely connected to the poleward flow of South Atlantic Central Water (SACW) across the shelf break. Together, these strong subsurface nepheloid layers are indicators of intensive lateral particle transport from the outer shelf towards a depocenter of organic matter on the upper continental slope.     

春季长江口外上升流的月际变化——以123°E断面为例

上升流是长江口外海域的重要水文现象,为深入了解该海域上升流的活动特征及其月际变化,于2015年春季(4月、5月和6月)对长江口外海域的水文环境进行逐月综合调查,并以123°E断面为例进行分析。结果显示,在春季调查期间,长江口外海域始终存在上升流现象,是由台湾暖流挟带底层高盐海水自南向北不断推进,并在长江口外海域沿海底斜坡涌升而形成。上升流强度在春季逐月增大,表现为:上升流涌升高度逐月变浅,至6月高盐上升流水体的涌升高度已普遍抬升到约15 m以浅水层,最高达到约10 m水深处;其影响范围不断向北扩展。春季,上升流活动区上层海水的温、盐特征逐渐由相对低温、高盐转变为高温、低盐;位于下层的上升流水体的温、盐特征比较稳定,变化幅度较小;上升流活动区的温、盐跃层现象总体呈现出逐月增强的趋势,盐度跃层现象尤为显著,其水平分布呈现出自南向北逐月扩大的变化趋势;跃层深度不断抬升。调查结果的月际变化特征表明,台湾暖流北进强度的逐月增大是导致春季长江口外上升流活动不断增强的主要因素;随着春季低盐长江冲淡水的强度和范围逐月增大,其与下层上升流挟带的高盐涌升水之间的跃层效应逐渐增强,对下层上升流的涌升有抑制作用;春季苏北沿岸流活动对该海域上升流现象的影响不显著。     

Low CO2 concentrations in the Gulf of Guinea during the upwelling season in 2006

The fugacity of CO₂ (fCO₂) was measured underway from 27 May to 5 July 2006 in the Gulf of Guinea when the upwelling conditions were taking place. The equatorial and the coastal upwellings are responsible for the large CO₂ outgassing observed in the tropical Atlantic. The highest fCO₂ (655 μatm) was measured in the eastern coastal upwelling. However, area of low fCO₂ are also observed. Those occurred north of 2°N, in the Guinea Current, and near 6°S close to the coast due to the Congo River discharge. The decrease of salinity is a major factor explaining low fCO₂. In the South Equatorial Counter Current region, south of 6°S near 10°W, low fCO₂ are not related to a salinity effect as this region is subject to excess evaporation. A comparison with the meridional transects of the RMS St Helena made in 1995–1996 near 15°W suggests that these low fCO₂ or even slight undersaturations can be observed from about 4°S to 10°S. It seems that they occur mainly in boreal summer. They could be caused by transport of water that has been in contact with the atmosphere long enough to come close to equilibrium. The low fCO₂ area are not reproduced by the CO₂ climatology probably because of the coarse resolution and the lack of data in this region. Despite the low fCO₂ area observed in 2006, the ΔfCO₂ in 2006 is higher than the 1995 climatology for the region 10°S–2°N, 10°W–10°E suggesting that fCO₂ is increasing over time but from the few cruises available, it is difficult to definitely conclude.     

Sedimentary records of eutrophication in the Changjiang Estuary upwelling area over last 100 a

The upwelling area in the Changjiang Estuary was selected to collect the core, where the red tide occurred frequently and hypoxic existed. The total organic carbon （TOC）, total nitrogen （TN）, biogenic silica （BSi） and stable organic carbon isotopic ratios（δ13 Corg） were determined on the 210pb-dated sediment core. The concentrations of TOC, TN, BSi as well as their sedimentation fluxes have in- creased to some extent since the 1970s. TOC and TN fluxes increased about 45%, 36% respectively. The average δ13 Coorg value in the core was -23.67 ×10^-3 which remained nearly constant before the 20 century. The δ13 Corg values increased after the 1900s, two marked increases were observed from the 1950s and the 1970s. A simple δ13 Cors model was used to estimate the contribution of terrigenous and marine organic matter inputs for the sediment, which indicated the increase in accumulation since the 1970s has been almost exclusively marine. The increasing of marine organic matter accumulation （TOC, TN and BSi） was corresponding with the increasing of fertilizer consumption and the NO3-N budgets from the Changjiang River. The riverine runoff of fertilizers and nutrients stimulated the algae blooming. Enhanced primary production resulted in an enrichment of organic matter in the sediment. These data support the hypothesis that anthropogenic nutrient loading has been a significant factor on the eutrophication in the Changjiang Estuary.     

长江口上升流区营养盐的分布及其通量的初步估算

根据2004年5月份长江口调查资料,分析了春季长江口上升流现象及其对营养盐分布的影响;初步估算了春季上升流的营养盐通量。结果表明:在春季,低温、高盐、低溶解氧的上升流稳定存在于122°20′～123°00′E,31°00′～32°00′N海区的10m 层和底层之间,并可以涌升到10m 层以上海区。上升流为上层海区输入了丰富的 PO_4-P 和相对低浓度的 NO_3-N 和 SiO_3-si。对上升流营养盐通量的计算表明,春季上升流中磷酸盐输送通量远高于长江径流输入,可能会成为影响该海区磷酸盐分布以及浮游植物生长的一个值得关注的因素:而氮和硅营养盐则不如长江径流输入量大。     

下扬子中二叠统上升流相与烃源岩的关系研究

下扬子区面积177020km^2,包括江苏、浙江、安徽、江西和上海绝大部分地区,这一区域的构造属性为被动大陆边缘,通过对该区古生界中二叠统的几十条剖面的实测、分析和对比,得出该区古生界中二叠统地层中的黑色碳质页岩、硅质页岩、硅质岩、硅质条带和结核以及磷矿层和磷结核等沉积是古特提斯海中上升流作用形成的。上升流水体中富营养盐和SiO2在古生代低纬度的下扬子地块生物大量繁殖,引发缺氧事件,形成上述硅质和磷质沉积以及有机质丰富的烃源岩、石煤和磷矿层等,由于上升流水体富营养盐和SiO2,生物化石属种丰富,个体大,多营底栖或固着浅海底生活,硅质生物放射虫等丰富。区内烃源岩有机质与上升流的强度呈正相关关系,可见它们之间存在着成因联系。     

On the reconstruction of upwelling history: Namibia upwelling in context

Eastern boundary upwelling is an important aspect of the modern ocean, despite the relatively small area involved. Consequences of increased upwelling during the Neogene, as a result of intensifying trade winds, include increased heat transport by the ocean, increased mixing, increased fractionation of phosphate from silicate, and opportunities for evolution of new species. Coastal upwelling has been studied since the first decade of the 20th century. The processes involved are complex, and differ depending on geographic setting. Off Namibia, upwelling history has been studied by a number of drilling expeditions; the last of these was ODP Leg 175, which occupied seven sites on the continental slope between Walvis Ridge and Cape Town, during September and October of 1997. Productivity proxies all along southwestern Africa suggest the presence of increased upwelling and organic matter supply to the sea floor during glacial periods. At the same time, there is a decrease in the supply of diatoms and other siliceous plankton remains. This is the Walvis Opal Paradox, established through the contrasting results of studies by Diester-Haass (1985) and Oberhänsli (1991). We propose that the Walvis Opal Paradox is fundamental to the understanding of glacial–interglacial productivity fluctuations on a global scale. Furthermore, a central feature of the history of late Neogene upwelling off Namibia is the Matuyama Opal Maximum, centered between Gauss and Olduvai magnetic chrons [Wefer et al., Proc. ODP 175 (1998)]. It is due to the fact that diatom supply first increases (during the Gauss) when the planet cools and then decreases again during additional cooling, on entering the Quaternary. On a 400 000-year scale, peak productions are coincident with (or slightly lag) maximum seasonal contrast potential in the high-latitude insolation curve. We suggest that this is further evidence that the nutrient content of thermocline waters was diminished during glacial periods. The reasons why this should be so remain to be discovered.     

Plankton dynamics and carbon flux in an area of upwelling off the coast of Morocco

A carbon flux study was carried out off the coast of Morocco, at 31°N, in a region characterized by the presence of a persistent cyclonic eddy. Two short-term (4 and 3 day) deployments of free-floating sediment traps were combined with water column sampling and rate process measurements as the ship followed the traps. For a period of 36 h between trap deployments, a hydrographic section was run along 31°30'N as part of a larger scale survey being carried out simultaneously on the R.V. A. von Humboldt. The first trap deployment was near the eastern margin of the eddy and the traps moved to the north and west in a frontal jet associated with its northern boundary. After the second deployment, which was at the recovery point of the first, the traps moved to the west and then to the southwest. Throughout the study, chlorophyll concentrations varied between 27 and 125 mg m⁻² (0–100 m), with highest concentrations in the upwelled water nearest the coast and in upwelled water generated within the cyclonic eddy. Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations were relatively uniform (13.6±1.8 and 1.63±28 g m⁻² with phytoplankton carbon accounting for 16–85% of total POC. Bacterial carbon was 5% of total POC and mesozooplankton carbon concentrations were equivalent to 9% of total POC. Microzooplankton biomass was not assessed but POC:PON ratios in the water column were often high, suggesting there was sometimes a large detrital component in the POC. Primary production rates varied between 1.0 and 2.5 g C m⁻² day⁻¹. Bacterial consumption accounted for 50% of primary production. Metabolic rates suggested that copepods were ingesting more than 0.4 g C m⁻² day⁻¹. while filtration rates suggested that ingestion of phytoplankton carbon was only 0.2 g C m⁻²day⁻¹, even when phytoplankton constituted 85% of the POC. f-ratios (based on uptake rates for ¹⁵N-nitrate and ammonia) were between 0.1 and 0.4, and excretion by mesozooplankton could account for 40% of the daily ammonium uptake by phytoplankton. HPLC pigment analysis showed that when chlorophyll biomass was high, diatoms were dominant, whereas when it was low, small prymnesiophytes, chlorophytes and diatoms were all important. The composition of the fluoresecent pigments in material in the sediment traps indicated that intact phytoplankton and copepod faecal pellets were the main sources but the relative rates of sedimentation of pigment, POC and PON for the two trapping periods did not reflect differences that were observed in the overlying water column. This was likely to be the result of spatial heterogeneity and strong horizontal currents heterogeneity and strong horizontal currents within the euphotic zone. Thus, material collected at 100 m probably did not originate in the water column immediately overlying the traps and trapping efficiencies might also have been variable.     

2004年夏季台湾海峡上升流海域悬浮颗粒物粒径谱分析

利用2004年夏季台湾海峡南部海域的现场激光粒度仪剖面测量数据,运用海洋食物链的粒径谱理论,分析了悬浮颗粒物的Sheldon谱图和正态化谱图的剖面分布精细结构。横跨台湾海峡沿岸及浅滩外斜上升流的A和B两断面Sheldon粒径谱类型相近,正态化谱图的斜率r的范围从-0.79到-0.65,在明显高于寡营养海域的水平上波动。斜率r的高值带或高变幅带,在上升流系高叶绿素带及叶绿素最大层的周边或前端的呈斑状分布。海洋食物链的粒径谱分析结果支持关于台湾海峡南部上升流生态系高生产力、短食物链和高营养转换效率的宏观认识,并深化对营养转换效率分布精细结构的了解。现场激光粒度仪可发展为探索海洋食物链时空分布精细结构的常备传感器。     

Coastal upwelling in the Gelendzhik area of the Black Sea: Effect of wind and dynamics

Long series data of a thermistor chain in the Black Sea coastal zone near Gelendzhik were analyzed. A thermistor chain installed 1 km offshore and at a depth of 22 m. There are full and incomplete upwelling events observed. The study of upwelling genesis based on: wind speed data from the NCEP/CFSR reanalysis and Gelendzhik weather station, velocity and direction of coastal currents measured by ADCP profiler moored on the bottom near the thermistor chain. Over the whole observation period (warm seasons of 2013–2015), more than 40 events of upwelling were registered four of them were full upwellings, when presence of under-thermocline water was observed near the sea surface. For every upwelling event, conditions prior to the changes in thermic structure, were analyzed. It is found that full upwelling generally occur under synergistic wind and current forcing. Fairly strong forcing of one of these factors is sufficient for partial upwelling to occur.     

Southward extension of the reproductive range of Macroramphosus scolopax in the upwelling area off North-West Africa

Ichthyological literature gives the distribution of M. scolopax as along the whole coast of West Africa. However, analysis of this literature and the results of trawling surveys in the North-East Atlantic suggest only exceptional occurrences in the tropics. Plankton surveys off N.W. Africa, up to and including 1977, rarely yielded M. scolopax larvae off the coast of the southern Sahara and not at all off Mauritania, though a few specimens were collected after having been swept southwards in the open ocean by the Canary Current. Larvae did occur off northern Mauritania in February 1983. Details of distribution, abundance and length composition of early stages caught during the period January–April 1983 are given. It is concluded that the reproductive range of M. scolopax (as well as that of some other temperate species) extends south of that documented and that its spawning season there may be shorter than in the centre of this species' distribution. The findings are discussed in relation to interannual variation of upwelling intensity and the current system off N.W. Africa.     

Pelagic nitrogen dynamics in the Vietnamese upwelling area according to stable nitrogen and carbon isotope data

Upwelling and nitrogen (N) fixation provide new N for primary production off southern central Vietnam. Here we evaluate the roles of both N sources for zooplankton nutrition by comparing δ¹⁵N and δ¹³C values in nitrate, particulate organic matter (POM), and six net-plankton size fractions from monsoon and intermonsoon seasons. The δ¹³C values in POM and the net-plankton size fractions differed by 2–4‰ at any time. We assume that plankton from the POM filters was dominated by nano-and picoplankton as opposed to micro- and mesoplankton in the net-samples. The implications of this are discussed in terms of size differential pathways of C and N in the planktonic food web. We used δ¹⁵N to estimate the differences in N nutrition between the actual upwelling region and the oligotrophic area further offshore. The δ¹⁵N values of the net-plankton size fractions were depleted in δ¹⁵N by ca. 2‰ outside compared to inside the upwelling area during the monsoon season. We attribute these patterns to the additional utilization of N derived from N fixation. The concomitant findings of high N fixation rates reported earlier and low subthermocline nitrate (nitrate_sub) values of 2.9–3.6‰ support this conclusion. Net-plankton δ¹⁵N values increased with size, pointing to the dominance of higher trophic levels in the larger size fractions. According to a two source mixing model N fixation may have provided up to 13% of the N demand in higher trophic levels.