NotesBenthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b     

南海东沙海域HD319岩心富甲烷环境底栖有孔虫群落结构

对南海东北部东沙海域HD319岩心富甲烷环境和非富甲烷环境底栖有孔虫进行对比研究,旨在探讨富甲烷环境对底栖有孔虫群落结构的影响。结果表明,该岩心富甲烷环境和非富甲烷环境的底栖有孔虫组成有所差异:富甲烷缺氧环境底栖有孔虫群落中耐低氧类内生种群占绝对优势,Uvigerina(U.peregerina,U.hispido-costata,U.rugosa,U.probscidea,U.spp.),Bulimina(B.aculeata,B.mexicana),Bolivina(B.bradyi,B.quadrilatera),Globocassidulina subglobosa,Brizalina superba,Hoglundina elegans等冷泉甲烷相关种大量出现;非富甲烷一般低氧环境下底栖有孔虫以内生种含量占优势,表生种和旋向种零星出现;富氧环境下底栖有孔虫以表生种和旋向种占优势,受有机碳含量变化控制明显。推测底栖有孔虫这种群落结构的差异是适应高甲烷含量的结果,底栖有孔虫对富甲烷环境的响应通过群落结构的差异表现出来。     

Bottom foraminiferal assemblages in the Deryugin Basin (Sea of Okhotsk) during the past 26000 years

Benthic foraminifers from a core of bottom sediments obtained in the Deryugin Basin at a depth of 1750 m were examined. Three distinct benthic foraminiferal assemblages that replaced one another throughout the last 26000 years were recognized. The assemblage dominated by Alabaminella weddellensis, Uvigerina auberiana, and Cassidulina translucens dwelled here from 26 to 24 ky B.P. The sediments of the glacial period between 26 and 12.18 ky B.P. contain no benthic foraminifers. The composition of the sediments suggests the existence of active bottom vents of gas-bearing fluids during that time. The dominance of Brizalina spissa, Uvigerina peregrina, and Cassidulina laevigata is characteristic of the period from 12.18 to 7 ky B.P., when the productivity of the surface waters in the region was high, and warm, poorly oxygenated waters spread over the bottom of the basin. During the past 7 000 years, the bottom conditions in the sea were similar to the present-day conditions and an assemblage with the dominance of Gyroidina orbicularis, Uvigerina auberiana, and Cassidulina teretis developed in the region.     

Sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera: A case study from Lisbon-Setúbal Canyon (southern Portugal)

Rose Bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern Portugal: one in the Lisbon-Setúbal Canyon and the other along the canyon edge. The total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry. Nitrate was used as a redox indicator, sedimentary chlorophyll a and CPE (chloroplastic pigment equivalents) contents as a measure of labile organic matter, and total organic carbon as a measure of bulk organic matter availability.The canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge. Water depth seemed to control sedimentary phytopigment content, but not total organic carbon. No significant correlation was seen between pigment and total organic carbon content.The abundance of calcareous foraminifera correlated with the phytodetritus content, whereas a weaker correlation was observed for the agglutinated taxa. Therefore, calcareous foraminifera appear to require a fresher food input than agglutinated taxa. The foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment, in line with the TROX concept. Phytopigment-rich (surficial CPE content >20 μg/cm³) sediments with a shallow nitrate penetration depth (∼1 cm depth) were inhabited by generally infaunal species such as Chilostomella oolina, Melonis barleeanus and Globobulimina spp. As the nitrate penetration increased to ∼2 cm depth in sediment and the pigment content remained relatively high (>15 μg/cm³), Uvigerina mediterranea and Uvigerina elongatastriata became dominant species. With declining CPE content and increasing nitrate penetration depth, the foraminiferal assemblages changed from the mesotrophic Cibicides kullenbergi-Uvigerina peregrina assemblage to the oligotrophic abyssal assemblage, mainly consisting of agglutinated taxa.     

Benthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out.The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth.Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough.From continental shelf edge to the bottom of Okinawa Trough,benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages:(1) Continental shelf break assemblage,dominated by Cibicides pseudoungerianus,corresponds to subsurface water mass of the Kuroshio Current;(2) upper continental slope assemblage,dominated by Cassidulina carinata,Globocassidulina subglobosa,corresponds to intermediate water mass of the Kuroshio Current;(3) intermediate continental slope assemblage,dominated by Uvigerina hispida,corresponds to the Okinawa Trough deep water mass above the carbonate lysocline.     

Abrupt changes of intermediate-water oxygen in the northwestern Pacific during the last 27 kyr

An oxygen minimum zone (OMZ) currently exists at intermediate water depths on the northern Japanese margin in the northwestern Pacific. The OMZ results largely from a combination of high surface–water productivity and poor ventilation of intermediate waters. We investigated the late Quaternary history (last 27 kyr) of the intensity of this OMZ using changes in benthic foraminiferal carbon isotopes and assemblages in a sediment core taken on the continental slope off Shimokita Peninsula, northern Japan, at a water depth of 975 m. The core was located well within the region of the present-day OMZ and high surface–water productivity. The benthic foraminiferal δ¹³C values, which indicate millennial-scale fluctuations of nutrient contents at the sediment–water interface, were 0.48‰ lower during the last glacial maximum (LGM) than during the late Holocene. These results do not indicate the formation of glacial intermediate waters of subarctic Pacific origin, but rather the large contribution of high-nutrient water masses such as the Antarctic Intermediate Water, implying that the regional circulation pattern during the LGM was similar to that of modern times. Benthic foraminiferal assemblages underwent major changes in response to changes in dissolved oxygen concentrations in ocean floor sediments. The lowest oxygen and highest nutrient conditions, marked by dysoxic taxa and negative values of benthic foraminiferal δ¹³C, occurred during the Bølling/Allerød (B/A) and Pre-Boreal warming events. Dysoxic conditions in this region during these intervals were possibly caused by high surface–water productivity at times of reduced intermediate–water ventilation in the northwestern Pacific. The benthic assemblages show dysoxic events on approx. 100- to 200-year cycles during the B/A, reflecting centennial-scale productivity changes related to freshwater cycles and surface–water circulation in the North Pacific.     

早第四纪西太平洋底栖有孔虫群与大洋深层水环流演化的关系

选取赤道西太平洋ODP 807站位(3°36.42'N,156°37.49'E,水深2 803.8 m,岩心长822.9 m)26.27~43.02 mbsf层段中的底栖有孔虫进行研究,以便了解早更新世2.5~1.6 Ma BP时期古生产力和深水环流的变化。结果显示,这一时期底栖有孔虫堆积速率(BFAR)、表生种和内生种比值(E/I)、Uvigerina spp.百分含量和有机碳百分含量(TOC%)等替代指标反映了西太平洋古生产力总体上呈现冰期高、间冰期低的特点,而其中Bulimina alazanensis的丰度变化则相反,反映了该种有可能更适合温暖、低营养的底层水环境。2.5~1.6 MaBP时期底栖有孔虫在丰度上以Uvigerina spp.为主,指示了早更新世西太平洋深层水受北部水团的控制更强。     

Tracing seafloor methane emissions with benthic foraminifera: Results from the Ana submarine landslide (Eivissa Channel,Western Mediterranean Sea)

The hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core KS16 from the headwall of the Ana submarine landslide in the Eivissa Channel, Western Mediterranean Sea. The core MS312 from a nearby location with no known methane emissions is utilised as control. The core was analysed for biostratigraphy, benthic foraminiferal assemblages, Hyalinea balthica and Uvigerina peregrina carbon and oxygen stable isotope composition, and sedimentary structures. The upper part of the core records post-landslide deglacial and Holocene normal marine hemipelagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment. In this interval, the δ¹³C composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core. Below the sedimentary hiatus caused by the emplacement of the slide, the foraminiferal assemblages are characterised by lower density and higher Shannon Index. Markedly negative δ¹³C shifts in benthic foraminifera are attributed to the release of methane through the seabed. The mean values of the ¹³C anomaly in U. peregrina are ? 0.951 ± 0.208 in the pre-landslide sediments, and ? 0.269 ± 0.152 in post-slide reworked sediments deposited immediately above the hiatus. The δ¹³C anomaly in Hyalinea balthica is ? 2.497 ± 0.080 and ? 2.153 ± 0.087, respectively. To discard the diagenetic effects on the δ¹³C anomaly, which could have been induced by Ca–Mg replacement and authigenic carbonate overgrowth on foraminifera tests, a benthic foraminifera subsample has been treated following an oxidative and reductive cleaning protocol. The cleaning has resulted, only in some cases, in a slight reduction of the anomaly by 0.95% for δ¹³C and < 0.80% for δ¹⁸O. Therefore, the first conclusion is that the diagenetic alteration is minor and it does not alter significantly the overall carbon isotopic anomaly in the core. Consequently, the pre-landslide sediments have been subject to pervasive methane emissions during a time interval of several thousand years. Methane emissions continued during and immediately after the occurrence of Ana Slide at about 61.5 ka. Subsequently, methane emissions decreased and definitely ceased during the last deglaciation and the Holocene.     

Stable isotopes in deep-sea living (stained) foraminifera from the Mozambique Channel (eastern Africa): multispecies signatures and paleoenvironmental application

Oxygen and carbon isotopes (δ¹⁸O and δ¹³C) have been investigated in carbonate tests of deep-sea foraminifera living in the Mozambique Channel (eastern Africa) to understand how environmental constraints (e.g., organic matter, oxygenation) control the intra- and interspecific variability of isotopic signatures. 197 living individuals, including eight different species, from various microhabitats within the sediment were sorted from sediment samples gathered at two stations on the Malagasy upper slope. Results show that the δ¹⁸O values of foraminiferal taxa were not controlled by microhabitat pattern. They presented tremendous and intriguing intraspecific variability that is not explained by the classical ontogenetic effect. The δ¹³C values of infaunal foraminiferal taxa do not show a 1:1 relationship with the bottom water δ¹³C DIC and do not present a constant offset from it; instead, they appear to be mainly controlled by a microhabitat effect. The lower δ¹³C values of shallow, intermediate, and deep infaunal taxa at the deeper station compared to those seen at the shallower station reflect the enhanced exportation of sedimentary organic matter at the sediment–water interface, and its related mineralization within the upper sediments. The ?δ¹³C between shallow/very shallow infaunal species (i.e., Hoeglundina elegans, Uvigerina hispida) and intermediate/deep infaunal species (i.e., Melonis barleeanus, Globobulimina barbata) permits insight into (1) the exportation of organic matter to the seafloor and (2) the various degradation pathways for organic detritus in the benthic environments off NW Madagascar.     

Répartition des foraminifères benthiques actuels sur le plateau continental sénégalais au sud de Dakar

Two hundred and twenty-four benthic foraminiferal species were recognized in the total assemblages of fifty samples collected from the Senegalese continental shelf south of Dakar (down to a depth of 200 m). A factor analysis based on nineteen dominant species shows three main factors. The first two seem to be associated with temperature and its seasonal variations; they are depth-related and determine two main faunal changes. The third factor is substrate-related. The main depth-related species are: i) Cribrononion gerthi, Quinqueloculina akneriana, Quinqueloculina lamarckiana, Cribrolinoides curtus, Elphidium fichtellianum and Textularia sagittula in the coastal zone; ii) Discorbinella bertheloti, Cancris aff. C. sagrum, Textularia truncata, Nonion fabum, Bulimina elegans and Hanzawaia solei in the inner shelf; iii) Trifarina bradyana, Trifarina fornasinii, Uvigerina peregrina and Cassidulina laevigata in the outer shelf. The species that are substrate-related are: i) N. fabum, B. elegans, C. gerthi and H. solei in the fine-grained sands and ii) Lobatula lobatula, C. curtus, T. sagittula and D. bertheloti in the coarse-grained sands. The reduction in planktonic percentage and diversity in the outer shelf are related to the upwelling seasonal influence.     

Impact of oil-based drill mud disposal on benthic foraminiferal assemblages on the continental margin off Angola

In order to assess the possible environmental impact of oily cuttings discharged during oil exploration activities, we studied the benthic foraminiferal faunas in a five-station, 4-km-long sampling transect around a cuttings disposal site at about 670 m depth offshore Angola (W Africa), where drilling activities started 1.5 years before sampling. Living (Rose Bengal stained) and dead foraminiferal faunas were sampled in March 2006. The faunal patterns mirror the spatial distribution of hydrocarbons, which are dispersed into a southeastern direction. Four different areas can be distinguished on the basis of the investigated faunal parameters (density, diversity and species composition of the living fauna, and comparison with subrecent dead faunas). The fauna at station S31, 300 m SE of the oil cuttings disposal site, appears to be clearly impacted: the faunal density and diversity are maximal, but evenness is minimal. Taxa sensitive to organic enrichment, such as Uvigerina peregrina, Cancris auriculus and Cribrostomoides subglobosus, have largely disappeared, whereas the low-oxygen-resistant taxon Chilostomella oolina and opportunistic buliminids and bolivinids attain relatively high densities. At station S32, 500 m SE of the disposal site, environmental impact is still perceptible. The faunal density is slightly increased, and U. peregrina, apparently the most sensitive species, is still almost absent. The faunas found at 1 and 1.8 km SE of the disposal site are apparently no longer impacted by the drill mud disposal. Faunal density and diversity are low, and the faunal composition is typical for a mesotrophic to eutrophic upper slope environment. Finally, Station S35, 2 km NW of the disposal site, contains an intermediate fauna, where both the low-oxygen-resistant C. oolina and the more sensitive taxa (U. peregrina, C. auriculus and C. subglobosus) are present. All taxa live close to the sediment–water interface here, indicating a reduced oxygen penetration into the sediment. Since the hydrocarbon concentration is low at this station, it appears that the faunal characteristics are the consequence of a slightly different environmental setting, and not due to a contamination with drill cuttings. Our data underline the large potential of benthic foraminifera as bio-indicators of anthropogenic enrichment in open marine settings, such as caused by the disposal of oily drill cuttings. The foraminiferal faunas react essentially by a density increase of a number of tolerant and/or opportunistic taxa, and a progressive disappearance of more sensitive taxa in the most impacted area. Rather surprisingly, large-sized taxa appear to be more sensitive than small-sized foraminiferal taxa.     

South Atlantic and benthic foraminifer δ13C deviations: implications for reconstructing the Late Quaternary deep-water circulation

Benthic foraminifer species Cibicidoides wuellerstorfi and related genera are assumed to secrete calcite very close to the carbon isotope values of the ambient bottom-water ΣCO₂. Recently, attention has been focused on substantial productivity-linked δ¹³C depletions. To examine further the productivity effect on benthic δ¹³C deviations, we present data from the South Atlantic between 15 and 35°S, including water samples from 10 hydrographic stations and related surface-sediment measurements on C. wuellerstorfi. We compare open-ocean data with observations in the Namibia Upwelling area. As a result, δ¹³C_ΣCO2 values as well as phosphate concentrations in water samples of the upwelling realm differ significantly from those of the open-ocean realm at least in the upper and mid-depth water masses (SACW, AAIW, UCDW). However, deviations from the Redfield fractionation, caused by air–sea fractionation, remain constant within each water mass, which means that the carbon isotope changes toward upwelling areas are exclusively determined by biological cycling. In addition to lower δ¹³C_ΣCO2 values in upwelling areas, a depletion in the δ¹³C of epibenthic foraminifer calcite is observed, which is most likely explained by the decay of organic matter, reducing the ¹³C/¹²C ratio in the pore water and influencing the carbon isotopic composition of the C. wuellerstorfi shells of highly productive areas. The paleoceanographic implication of this effect for reconstructing the Late Quaternary deep-water circulation is discussed using carbon isotope records of several sediment cores within and outside the Namibia upwelling area.     

Foraminifera in surface sediments of the Bering and Chukchi Seas and their sedimentary environment

Based on a quantitative analysis of foraminifera in 39 surface samples of the Bering andChukchi Seas, the nearly absence of planktonic foraminifera in the surface sediments can be related to the low surface primary productivity and strong carbonate dissolution in the study area. It has been revealed that the surface primary productivity, and carbonate dissolution and properties of water masses related to the water depth mainly control the distribution of benthic foraminifera. The shelf of the Chukchi Sea is dominated by the Elphidium spp. assemblage and Nonionella robusta assemblage with low foraminiferal abundance and diversity, which is controlled by the coastal water mass of the Arctic Ocean. The slope of the Bering Sea is dominated by the Uvigerina peregrina - Globobulimina affinis assemblage with abundant N. robusta, and relatively high foraminiferal abundance and diversity, which is controlled by the intermediate and deep water masses of the Pacific Ocean. However, the Bering Sea has relatively sha     

Benthic foraminifera from the deep-water Niger delta (Gulf of Guinea): Assessing present-day and past activity of hydrate pockmarks

We present ecological and isotopic (δ¹⁸O and δ¹³C) data on benthic foraminifera sampled from 4 deep-sea stations in a pockmark field from the deep-water Niger delta (Gulf of Guinea, Equatorial Atlantic Ocean). In addition, a series of sedimentological and (bio)geochemical data are shown to back up foraminiferal observations. All stations are located within 1.2 km of each other, so prevailing oceanographic conditions can be assumed to be similar at each site. Two of the sites (GMMC-01 and GMMC-02) are located in a pockmark (named “pockmark A”) where current methane seepages were recorded by ROV observations. A third station (GMMC-03) is located in the topographic depression interpreted as a collapsed pockmark (named “pockmark B”). The fourth site (GMMC-04) is a reference station, without evidence of past or present seepages. Our observations show that degraded organic matter with low bio-availability is present at all stations with a preferential burial of organic compounds in topographic depressions (GMMC-03 station). Authigenic aragonite is abundant in surface sediments at stations GMMC-01 and -02. Its precipitation is likely related to high rates of methane oxidation during past seep events in episodically active pockmark A. In contrast, the absence of anaerobic methanotrophic Archaea (ANME) during the sampling period (November 2011) suggests that only moderate sulphide and methane oxidation take place close to the sediment–water interface. Compared to the reference site GMMC-04, living foraminifera at the collapsed and episodically active pockmarks show minor changes in terms of diversity, standing stocks and faunal composition. However, the δ¹³C signal of living and dead (but well-preserved) foraminiferal species (Ceratobulimina contraria, Melonis barleeanus, Uvigerina peregrina) is depleted in the episodically active pockmark A compared to the other stations. Overgrowth of authigenic carbonate on altered foraminifera generates an important shift to lower δ¹³C values. Dead faunas carry a complex time-averaged message, integrating taphonomic gains and losses related to the temporal variability of gas emission. They reveal major faunal differences that may be useful to detect gas hydrate seepages in different pockmark stages.     

长江口低氧区底栖有孔虫组合

对全球低氧区的分布、形成机制以及低氧区海水表层特征、海底地球化学特征、生物特征等进行了系统的描述。着重对全球低氧区的底栖有孔虫特征进行了分析、对比,并与长江口底栖有孔虫特征相结合,讨论适合指示长江口低氧区的底栖有孔虫组合,初步分析认为Epistominella naraensis(奈良小上口虫)、Bulimina marginata(具缘小泡虫)、Bolivina spp.(箭头虫诸种)、Florilus spp.(花朵虫诸种)、Ammonia spp.(卷转虫诸种)以及Bulliminella spp.(微泡虫诸种)为长江口低氧区的敏感种,具有低氧环境的指示意义,并可以作为古低氧事件研究的标志。但实际应用时应根据研究需要取合适的属种组合使用。     

厌氧沉积中有孔虫组合特征

厌氧沉积的有孔虫组合中,底栖有孔虫主要由Bolivina诸种和Buliminella tenuata组成,同时含有少量厌氧标志种Suggrunda eckisi;浮游有孔虫中以Globigerrina bulloides和G.quingueloba为数较多。底栖有孔虫与浮游有孔虫数量相比,浮游有孔虫数量很少。     

白令海和楚科奇海表层沉积中的有孔虫及其沉积环境

通过对白令海和北冰洋楚科奇海39个表层沉积样品中有孔虫的定量分析,发现表层沉积中浮游有孔虫稀少可能与该区表层生产力低、碳酸盐溶解作用较强有关,而底栖有孔虫的分布则主要受表层初级生产力以及与水深相关的碳酸盐溶解作用和水团性质所控制,其中北冰洋楚科奇海陆架区有孔虫以Elphidium spp.组合和Nonionella robusta组合为主,丰度和分异度低,受北冰洋沿岸水团控制;白令海陆坡区有孔虫以Uvigerina peregrina-Globobulimina affinis组合为主,含N.robusta较多,丰度和分异度相对高,受太平洋中层和深层水团控制,但该区碳酸盐溶跃层和补偿深度(CCD)相对浅,约分别位于2000和3800m处.此外,白令海陆坡上部表层沉积中含有北冰洋陆坡区典型深水底栖有孔虫种Stetsonia arctica,说明白令海峡两侧的海区曾有深部水交流.     

The ecology and distribution of benthic foraminifera at the Håkon Mosby mud volcano (SW Barents Sea slope)

To investigate a possible influence of submarine methane seepage on benthic foraminiferal communities, Rose Bengal stained (“live”) and empty tests of benthic foraminifera were studied from the sediment surface down to 15 cm sub-bottom depth of 12 sites at the Håkon Mosby mud volcano (HMMV). In addition, one reference site well away from the seep sites, but from similar water depths and the same general hydrographic setting was occupied for comparison. The HMMV is located at 1265 m water depth on the SW Barents Sea continental slope. Distinct living foraminiferal associations at the HMMV are linked to specific sedimentary, microbial, and macrofaunal habitats. In the center of the crater, and in crater areas completely covered by bacterial mats, Cassidulina reniforme is the only, albeit rare, living species. Below the top few millimeters, sediments are anoxic and devoid of living specimens. At the rim of the mud volcano, at sites densely populated by pogonophoran tube worms, three benthic foraminiferal associations are found; (i) a Fontbotia wuellerstorfi–Lobatula lobatula association living attached to the upper parts of pogonophoran tubes, which protrude into oxic water, (ii) a diverse Cassidulina neoteretis association populating dysoxic sediments of the surface centimeter, and (iii) a species-poor Bolivina pseudopunctata association colonizing the subsurface sediments down to four centimeters. Generally, we did not find endemic or seep indicative species or associations at the HMMV. However, the HMMV live faunas dominated by B. pseudopunctata are not found at the reference site nor are they described from comparable water depths and environments without gas seepages from the Norwegian-Greenland Seas.In the center and outer rim of the mud volcano, a C. neoteretis–Reophax guttifer dead association, similar to the one at the reference site, characterizes an assemblage of strongly corroded and partly displaced tests. At bacterial mat sites, a C. reniforme dead association corresponds to the living one. Thus both the living and the dead associations are indicative of a specific bacterial mat environment at the HMMV.     

Influence of seasonal primary productivity on δ13C of North Atlantic deep-sea benthic foraminifera

The stable isotopic composition of benthic foraminifera has been widely used to reconstruct deep-ocean circulation, but questions have been raised about the influence of organic carbon flux on the carbon isotopic composition of deep-sea taxa. We show that annual and seasonality of primary productivity in the North Atlantic do not affect δ¹³C of Planulina wuellerstorfi, but that the intermittency or seasonality of primary production has a significant effect (0.9‰ change over 60° latitude) on δ¹³C of Epistominella exigua, reflecting the influence of pelagic-benthic coupling and microhabitat preferences on test geochemistry. These results support the use of δ¹³C of P. wuellerstorfi in paleocirculation studies and suggest that the δ¹³C of E. exigua can be used to reconstruct seasonality of productivity.     

Upwelling and productivity along the Peru–Chile Current derived from faunal and isotopic compositions of planktic foraminifera in surface sediments

We report on the spatial distribution of isotopic compositions of the two planktic foraminifera species Globigerina bulloides and Neogloboquadrina pachyderma (dex.), and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the Chilean continental slope between 23°S and 44°S. Both δ¹³C and δ¹⁸O data of N. pachyderma (dex.) show little variability in the study area. North of 39°S, the isotopic values of N. pachyderma (dex.) are heavier than those of G. bulloides, whereas south of 39°S, this relation inverses. This is indicative for a change from a well-mixed, deep thermocline caused by coastal upwelling north of 39°S to well-stratified water masses in a non-upwelling environment south of 39°S. In addition, the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39°S to a high-nutrient-non-upwelling assemblage south of 39°S, which is characterized by decreased contributions of upwelling indicators such as G. bulloides, N. pachyderma (sin.), and Globigerinita glutinata. In general, we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23°S and 44°S off Chile. Our data point to higher marine productivity at upwelling centers north of 25°S and at 30–33°S. South of 39°S, significant supply of nutrients by fluvial input most likely boosts the productivity.