Increase In Export Production Research Articles

Elevated Post K‐Pg Export Productivity in the Gulf of Mexico and Caribbean

AbstractThe global heterogeneity in export productivity after the Cretaceous‐Paleogene (K‐Pg) mass extinction is well documented, with some sites showing no change on geologic timescales, some demonstrating sustained decline, and a few showing a somewhat surprising increase. However, observational data come from sites so widespread that a key outstanding question is the geographic scale of changes in export productivity, and whether similar environments (e.g., open ocean gyres) responded similarly or whether heterogeneity is unrelated to environment. To address this, we developed three new Ba/Ti export productivity records from sites in the Gulf of Mexico and Caribbean which, combined with published data from a fourth site in the Chicxulub Crater itself, allow us to reconstruct regional changes in post K‐Pg export productivity for the first time. We find that, on a regional scale, export productivity change was homogenous, with all four sites showing a ∼300 Kyr period of elevated export production just after the boundary, followed by a longer period of decline. Interestingly, this interval of elevated export production appears to coincide with the post K‐Pg global micrite layer, which is thought to at least partially have been produced by blooms of carbonate‐producing cyanobacteria and other picophytoplankton. Global comparison of sites shows that elevated export productivity appears to have been most common in oligotrophic gyres, which suggests that changing plankton ecology evidenced by the micrite layer altered the biological pump, leading to a temporary increase in export production in these settings.

Covariation of Deep Antarctic Pacific Oxygenation and Atmospheric CO2 during the Last 770 kyr

Abstract We present new geochemical evidence of changes in oxygenation of the deep Antarctic Pacific over the last 770 kyr. Our data are derived from redox-sensitive metals and export production proxies extracted from gravity core ANT34/A2-10 at 4217 m water depth. Our results show that oxygen levels in the deep Antarctic Zone (AZ) varied in line with the release of deeply sequestered remineralized carbon to the atmosphere during glacial–interglacial (G–IG) cycles, with lower oxygen concentrations and more carbon storage during glacial periods. Subsequent reductions in the amount of carbon stored at depth were closely associated with improved ventilation during glacial terminations. The systematic and repeated glacial-to-interglacial increases in export production in the AZ region indicate a robust pattern of enhanced Southern Ocean (SO) ventilation during interglacial periods. In addition to the decline in atmospheric CO2 caused by iron fertilization in the Subantarctic AZ (SAZ) during the latter half of the glacial progression, decreases in productivity in the central AZ suggest that the weakening of SO ventilation induced deep AZ carbon sequestration and that this might have made a continuous additional contribution to the CO2 decline from each interglacial peak to glacial maximum. Observed variations in the degree of deep oxygenation and “organic carbon pump” efficiency in the central AZ might be driven primarily by physical “ventilation” processes (i.e., overturning circulation, mixing, and/or air–sea gas exchange). Our records of abyssal oxygenation in the central AZ, which vary in concert with atmospheric CO2 levels over the last several G–IG cycles, provide strong evidence that SO ventilation plays a significant role in controlling variations in both the amount of respired carbon sequestered in the deep ocean and atmospheric CO2 concentrations on G–IG timescales. Specifically, we suggest that the “organic carbon pump” (OCP) in the SAZ and the physical ventilation processes in the AZ (the “carbon venting valve”) acted together synergistically, but dominated at different intervals over G–IG cycles, to repeatedly switch the SO between carbon sink and carbon source, thereby modulating the atmospheric CO2 over the last 770 kyr. These findings provide new insights into the role of the AZ in controlling deep SO carbon sequestration and atmospheric CO2 levels in G–IG cycles.

Last 10000 years Variation in the Intensity of OMZ-Core Reconstructed from Sediment of the Eastern Arabian Sea

The Arabian Sea Oxygen Minimum Zone (OMZ) is one of the most intense of the world ocean OMZs witnessing denitrification, hence, has implications to global climate. In order to understand the Holocene variations in the OMZ of this region, a sediment core (BP3-GCR3) from a water depth of 500 m was retrieved, which is presently swept by nearly anoxic waters of the core of the OMZ. The sedimentary oxide-bound Mn, a reliable redox proxy, exhibits a gradual decrease from ∼14 ppm during the early-Holocene to ∼8 ppm during the late-Holocene, suggesting a relatively less intense OMZ during the former period. The concentration of a suite of other redox-sensitive elements (Fe, Co and Ce) associated with the dispersed sedimentary oxide particulates also show a gradual and coherent decrease through the Holocene suggesting reduction of dissolved oxygen (DO) in the core of the OMZ towards the modern times. This intensification of OMZ seems to be a result of increased export production coupled with decreasing ventilation of thermocline waters through the Holocene. A one-time positive shift is observed at ∼5.5 ka BP in the organic carbon content (OC) from ∼2 % to ∼10 % in core-top. This shift in OC content is also marked by rapid decrease of CaCO3 by ∼20 %, suggesting enhanced carbonate dissolution due to increased anoxia in the OMZ core caused by increased export production in the late Holocene.

Toward an Improved Understanding of the Marine Barium Cycle and the Application of Marine Barite as a Paleoproductivity Proxy

Marine barite (BaSO4) is a relatively ubiquitous, though minor, component of ocean sediments. Modern studies of the accumulation of barite in ocean sediments have demonstrated a robust correlation between barite accumulation rates and carbon export to the deep ocean. This correlation has been used to develop quantitative relationships between barite accumulation rates and export production and is used to reconstruct export production in the geologic past, particularly during times of dynamic changes in the carbon cycle. We review the processes that affect the formation and preservation of marine barite, as well as those controlling the relationship between the barium (Ba) and carbon biogeochemical cycles. Additionally, we take a new approach to modeling the marine Ba cycle as a two-box model, specifically evaluating Ba utilization in the surface ocean and refining the equation describing the relationship between export production and barite formation. We compare these new results with past modeling efforts. The new model demonstrates that increases in export production can lead to sustained increases in barite accumulation in marine sediments without resulting in complete surface water Ba depletion, which is distinctly different from previous modeling results.

From Agroforestry to Agroindustry: Smallholder Access to Benefits From Oil Palm in Ghana and the Implications for Sustainability Certification

Oil palm production in Ghana—which is primarily cultivated by smallholders (60%+)—plays an important role in local economies and rural livelihoods. As a multi-functional crop, it is embedded in the everyday life of rural and urban Ghanaians both by individual households and on an industrial level. The sector is currently experiencing a resurgence under Ghana’s New Patriotic Party (NPP) rule and is being targeted by the Roundtable on Sustainable Palm Oil (RSPO) for yield intensification and increased export production. End goals of these efforts include poverty alleviation, environmentally responsible development efforts, and agricultural diversification in rural areas. We apply Ribot and Peluso’s “theory of access” (2003) to assess the barriers and opportunities for smallholder oil palm farmers, and the degree to which these are addressed by RSPO interventions. Our results highlight how Ghanaian smallholders gain many benefits from palm oil production as a source of regular income, a drought-resilient crop, and a source of cooking oil for household use. However, they also report different levels of access to finance, markets, land, and technical support, along with differing views and visions of the oil palm sector’s development. The focus of governmental and RSPO initiatives on international trade-based incentives overlooks this diversity and, in particular, the importance of local markets for Ghanaian livelihoods. This poses a threat to women millers and traders, poorer producers, and the local markets they supply who risk losing access to the palm oil supply chain. More generally, these findings illustrate the importance of understanding how markets interact at multiple local to international scales, in order to design interventions that will more equitably reach and benefit local communities.

Biomarker evidence for nitrogen-fixing cyanobacterial blooms in a brackish surface layer in the Nile River plume during sapropel deposition

Abstract Sapropels are organic-rich sediment layers deposited in the eastern Mediterranean Sea during precession minima, resulting from an increase in export productivity and/or preservation. Increased freshwater delivery from the African continent resulted in stratification, causing deepwater anoxia, while nutrient input stimulated productivity, presumably at the deep chlorophyll maximum. Previous studies have suggested that during sapropel deposition, nitrogen fixation was widespread in the highly stratified surface waters, and that cyanobacteria symbiotic with diatoms (diatom-diazotroph associations, DDAs) were responsible. Here we analyzed sapropel S5 sediments for heterocyst glycolipids (HGs) from three locations in the eastern Mediterranean. HG biomarkers can differentiate between those heterocystous cyanobacteria that are free living (found predominately in freshwater or brackish environments) and those that are from DDAs (found in marine settings). In our primary core, from a location which would have been influenced by the Nile River outflow, we detected a HG with a pentose (C5) head group specific for DDAs. However, HGs with a hexose (C6) head group, specific to free-living cyanobacteria, were present in substantially (up to 60×) higher concentration. These data suggest that at our study location, free-living cyanobacteria were the dominant diazotrophs, rather than DDAs. The C6 HGs increased substantially at the onset of sapropel S5 deposition, suggesting that substantial seasonal cyanobacterial blooms were associated with a brackish surface layer flowing from the Nile into the eastern Mediterranean. Two additional S5 sapropels were analyzed, one also from the Nile delta region and one from the region between Libya and southwestern Crete. Overall, comparison of the HG distribution in the three S5 sapropels provides evidence that all three locations were initially influenced by surface salinities that were sufficiently low to support free-living heterocystous cyanobacteria. While free-living heterocystous cyanobacteria continued to outnumber DDAs during sapropel deposition at the two Nile-influenced sites, DDAs, indicators of persistent marine salinities, were the dominant diazotrophs in the upper part of the sapropel at the more westerly site. These results indicate that N2 fixation by free-living cyanobacteria offers an important additional mechanism to stimulate productivity in regions with strong river discharge during sapropel deposition.

Multidecadal Changes in Marine Subsurface Oxygenation Off Central Peru During the Last ca. 170 Years

Subsurface water masses with permanent oxygen deficiency (oxygen minimum zones, OMZ) are typically associated with upwelling regions and exhibit a high sensitivity to climate variability. Over the last decade, several studies have reported a global ocean deoxygenation trend since 1960 and a consequent OMZ expansion. However, some proxy records suggest an oxygenation trend for the OMZ over the margins of the Tropical North East Pacific since ca. 1850. At the Tropical South East Pacific, the upper Peruvian margin is permanently impinged by a shallow and intense OMZ. In this study, we aim to 1) reconstruct the (multi)decadal oxygenation variability off central Peru, and 2) to identify the influence of both largescale and local factors and the potential underlying mechanisms driving subsurface oxygenation in the Eastern Pacific. We combined a multiproxy approach in multiple paleoceanographic records for the last ~170 years with instrumental records of subsurface oxygen concentrations since 1960. We analyzed benthic foraminiferal assemblages, redox-sensitive metals (Mo, Re, U), δ15N and contents of total organic carbon and biogenic silica in multiple sediment cores collected in the upper margin off Callao (180 m) and Pisco (~300 m). An OMZ weakening over the Peruvian central margin can be inferred from 1865 to 2004. The records can be divided in three major periods, based on responses of local productivity and subsurface ventilation: i) the mid to late nineteenth century, with enhanced siliceous productivity, a strong oxygen-deficient and reducing sedimentary conditions; ii) the late nineteenth century to mid-twentieth century, with less oxygen-deficient and reducing sedimentary conditions, superimposed to a slight decadal-scale variability; and iii) the late twentieth century until the early 2000’s, with a slight oxygenation trend. We attribute the centennial-scale oxygenation trend in the Tropical East Pacific to ventilation processes by undercurrents that decreased subsurface oxygenation even when during the same period an overall increase in export production was inferred off Peru. Unlike other upwelling areas in the Tropical East Pacific, subsurface oxygenation off Peru does not show a decrease in the last decades, instead a subtle oxygenation trend was observed close to the core of the OMZ at 200 m depth.

Last 35,000-year water column temperature and productivity variation in the Eastern Arabian Sea: monsoon and global climate connection

A radiocarbon-dated sediment core from the flat top of Wadia Guyot at a 1500-m water depth in the Eastern Arabian Sea (EAS), western margin of India, preserves the records of past changes in water column temperatures and surface productivity. The time-series of oxygen isotope record extracted from planktonic foraminifera Globigerinoides (G.) sacculifer allows us to identify the Last Glacial Maximum (LGM, Ave. + 0.3 ‰: ~ 28–20 ka), the deglacial transition (a decrease from + 0.3‰ to − 1.2‰: ~ 20–11 ka), and the Holocene intervals (Ave. − 1.2‰: ~ 11–5 ka). The LGM cooling of the mixed layer by ~ 2 °C, thermocline by ~ 3 °C, and bottom water by ~ 4 °C is evident. The commencement of deglacial warming of the mixed layer lags thermocline warming by ~ 1 ky and bottom water warming by ~ 3ky. As different water masses of local and remote origin occur at different depths in the EAS, the observed offsets in timing and magnitude of changes in the temperatures through deglaciation indicate their independent behavior to past climate variation. The time-series of Corg, n-alkanes, and abundance of Uvigerina spp. exhibit distinct enrichments during the LGM as compared to Holocene (~ 1.7% vs 1.1%; ~ 1800 ng/g vs 1200 ng/g and ~ 20 vs < 5 tests/g of coarse fraction, respectively), which suggest enhanced surface productivity and accordingly increased export production.

Increased export production during recovery from the Paleocene–Eocene thermal maximum constrained by sedimentary Ba isotopes

The Paleocene–Eocene thermal maximum (PETM; ∼56 Ma) was a transient global warming event associated with a huge perturbation to the global carbon cycle. Changes in marine biological productivity may have contributed to the rapid recovery from this climate change event, by driving the burial of inorganic and organic carbon. Disagreement between proxy reconstructions, however, makes the response of biological productivity to climatic changes experienced during the PETM uncertain. Accumulation of non-detrital barium (Ba) in marine sediments is a commonly used proxy for export production. This proxy however can be compromised by artifacts resulting from dilution and changes in barite preservation, issues that have been debated for its application to sediments deposited during the PETM. Here we present a new approach to address these limitations, by combining non-detrital Ba accumulation with Ba isotope data for marine PETM sediments. Observed positive correlation between these variables is consistent with their control by local changes in export production. These results help resolve previous discrepancies between productivity reconstructions, and indicate export production at sites in the Southern Ocean and South Atlantic decreased or remained unchanged following the PETM onset, followed by an increase to maximum values in the PETM recovery period. This increase in export production coincides with elevated carbonate accumulation rates, representing an important mode of carbon sequestration. These new constraints therefore support the idea that increased production and export of calcifying nannoplankton, perhaps driven by changes in ocean stratification and/or terrestrial runoff, played an important role in rapid recovery from the PETM. This work also demonstrates the utility of sedimentary Ba isotope compositions for understanding past changes in the marine carbon cycle.

A Late Quaternary climate record based on long-chain diol proxies from the Chilean margin

Abstract. In this study we have applied different indices based on long-chain diols, i.e., the long-chain diol index (LDI) as a proxy for past SST, the diol index as an indicator of past upwelling conditions, and the nutrient diol index (NDI) as a proxy for nitrate and phosphate concentrations in seawater. The proxies were analyzed in marine sediments recovered at ODP Site 1234, located within the Peru–Chile upwelling system, with a ∼2 kyr resolution covering the last 150 kyr. We also generated TEX86H and U37K′ temperature and planktonic δ18O records, as well as total organic carbon (TOC) and accumulation rates (ARs) of TOC and lipid biomarkers (i.e., C37 alkenones, GDGTs, dinosterol, and loliolide) to reconstruct past phytoplankton production. The LDI-derived SST record covaries with TEX86H- and U37K′-derived SST records as well as with the planktonic δ18O record, implying that the LDI reflects past SST variations at this site. TOC and phytoplankton AR records indicate increased export production during the last interglacial (MIS 5), simultaneous with a peak in the abundance of preserved Chaetoceros diatoms, suggesting intensified upwelling during this period. The diol index is relatively low during the upwelling period, but peaks before and after this period, suggesting that Proboscia diatoms were more abundant before and after the period of upwelling. The NDI reveals the same trends as the diol index, suggesting that the input of nitrate and phosphate was minimal during upwelling, which is unrealistic. We suggest that the diol index and NDI should perhaps be considered as indicators for Proboscia productivity instead of upwelling conditions or nutrient concentrations.

Neogene Benthic Foraminiferal Biofacies, Paleobathymetry, and Paleoenvironments of a Gulf of Mexico Transect

AbstractWe document Neogene benthic foraminiferal biofacies changes on a depth transect of six Gulf of Mexico industry wells (sidewall and cutting samples) that is oblique to the coast and extends from Main Pass to Green Canyon (offshore Alabama to Louisiana, USA). Calcareous nannofossil and planktonic foraminiferal biostratigraphic control provides the framework to make interwell comparisons of the benthic foraminiferal biofacies; these comparisons provide the basis for paleobathymetric and paleoenvironmental interpretations and to identify useful benthic foraminiferal biostratigraphic markers in this region.Benthic foraminiferal faunas indicate that Neogene paleodepths were slightly shallower at the eastern wells and deepened towards the western wells. Calcareous benthic foraminiferal biofacies dominated by Uvigerina spp. indicate that paleoenvironments characterized by low-oxygen conditions and/or high productivity occurred periodically during deposition along the transect. This is supported by repeated occurrences of a distinctive assemblage of agglutinated foraminifera (known as the “Agua Salada Fauna”) that is typical of dysaerobic environments.Evidence of intensified low-oxygen/high-productivity environments are recorded in lowermost Middle Miocene sediments at some locations and are present at all wells in Upper Miocene deposits. In Upper Miocene-Pliocene sediments, oxygen levels appear to have been related to paleodepth, indicating that the development of lower oxygen conditions was the result of an expansion or migration of the oxygen minimum zone. Our results are consistent with a global cause for the expansion of the oxygen minumum zone during the Late Miocene and widespread increase in export production. Our study shows that despite problems in well cuttings (cavings, inconsistent sampling) and complications in regional salt and fault tectonics, well transects can provide coherent benthic foraminiferal biofacies patterns that reveal paleobathymetric and paleoenvironmental changes in the Gulf of Mexico.

Latest Cretaceous/Paleocene deep-sea ostracode fauna at IODP Site U1407 (western North Atlantic) with special reference to the Cretaceous/Paleogene boundary and the Latest Danian Event

Abstract During the Paleocene, the marine plankton community recovered its diversity after a severe diversity loss at the Cretaceous/Paleogene (K/Pg) boundary. In general, changes in Paleocene deep-sea ostracode faunas are poorly understood. It is still unclear how the deep-sea ostracode faunas changed during compelling events such as the K/Pg boundary (66.04 Ma) and the Latest Danian Event (LDE: ~ 62.18 Ma), a transient Paleocene warming event. In this report, we describe a study on the latest Cretaceous–Late Paleocene ostracodes from Integrated Ocean Drilling Program Site U1407, off Newfoundland, in the northwestern Atlantic. Thirty-six ostracode taxa were obtained from 202 discrete samples that were collected from the interval between 66.3 and 57.3 Ma. Near the K/Pg boundary, 8% (2 of 25) of the Maastrichtian taxa became extinct. The extinction rate is estimated to be at most 0.12 E MSY − 1 , which is equal to extinction rate of 12% per one million years and is in the same range as the background-level extinction rate. Comparing the extinction rates between different ocean basins such as Maud Rise and Blake Nose, the ostracode extinction at the K/Pg boundary displays striking geographical heterogeneity. Between the Maastrichtian and Danian, the ostracode faunas change from a biofacies dominated by shallow bathyal taxa to one dominated by deep bathyal taxa. During the LDE, ostracode faunas display an increase in their benthic ostracode accumulation rates and taxonomic diversity as well as an increase in the relative abundance of Krithe crassicaudata simultaneously with a decline in carbonate content. A similar change is commonly documented in fauna from the northeastern Atlantic during the Paleocene–Eocene Thermal Maximum (PETM; 56.0 Ma). In contrast to the PETM fauna, an extinction event is not recognized. Near the Danian/Selandian boundary, the ostracodes show an increase in export productivity. After the Danian, the ostracodes form a community that appears to tolerate warm and acidified water. Export productivity remains high during the Selandian and Thanetian.

Export production in the New-Zealand region since the Last Glacial Maximum

Increased export production (EP) in the Subantarctic Zone (SAZ) of the Southern Ocean due to iron fertilisation has been proposed as a key mechanism for explaining carbon drawdown during the last glacial maximum (LGM). This work reconstructs marine EP since the LGM at four sites around New Zealand. For the first time in this region, 230-Thorium-normalised fluxes of biogenic opal, carbonate, excess barium, and organic carbon are presented. In Subtropical Waters and the SAZ, these flux variations show that EP has not changed markedly since the LGM. The only exception is a site currently north of the subtropical front. Here we suggest the subtropical front shifted over the core site between 18 and 12 ka, driving increased EP. To understand why EP remained mostly low and constant elsewhere, lithogenic fluxes at the four sites were measured to investigate changes in dust deposition. At all sites, lithogenic fluxes were greater during the LGM compared to the Holocene. The positive temporal correlation between the Antarctic dust record and lithogenic flux at a site in the Tasman Sea shows that regionally, increased dust deposition contributed to the high glacial lithogenic fluxes. Additionally, it is inferred that lithogenic material from erosion and glacier melting deposited on the Campbell Plateau during the deglaciation (18–12 ka). From these observations, it is proposed that even though increased glacial dust deposition may have relieved iron limitation within the SAZ around New Zealand, the availability of silicic acid limited diatom growth and thus any resultant increase in carbon export during the LGM. Therefore, silicic acid concentrations have remained low since the LGM. This result suggests that both silicic acid and iron co-limit EP in the SAZ around New Zealand, consistent with modern process studies.

Geochemistry of Aegean Sea sediments: implications for surface- and bottom-water conditions during sapropel deposition since MIS 5

Piston cores collected from the Aegean Sea provide a record of sapropel sequence S1, S3-S5. Primary productivity calculations using the equations of Muller and Suess suggest surface paleoproductivities ranged from 180 to 995 g C m-2 year-1 for sapropels and from 40 to 180 g C m-2 year-1 for nonsapropel sediments with corresponding total organic carbon values of 9%-12% and 1%-3%, respectively. The higher paleoproductivities exceed those in the most fertile modern upwelling zones, so are probably overestimated. Instead, enhanced preservation, particularly for S4 and S5, likely resulted from poor bottom-water ventilation beneath a salinity-stratified water column. If the preservation factor in the equations of Howell and Thunell is increased to account for such conditions, more realistic paleoproductivity estimates ensue. The interpreted presence of a deep chlorophyll maximum layer for S3-S5 within the lower part of the photic zone may account for high marine organic carbon and increased export production. A deep chlorophyll maximum layer is not advocated for S1 because of the presence of N. Pachyderma (d) immediately below S1. The organic geochemical data show that both marine and terrestrial organic matter contributed equally to sapropels S3, S4, and S5. Sapropels S3-S5 were deposited under normal marine conditions with very limited and temporary establishment of near-euxinic bottom-water conditions. Highly depleted and somewhat uniform Δ34S values together with the absence of fully euxinic conditions during sapropel intervals suggest that bacterially mediated sulfate reduction took place consistently below the sediment-water interface. It is believed that climbing levels of primary productivity triggered the onset of sapropel deposition, but that other contemporaneous factors extended and enhanced the conditions necessary for sapropel deposition, including increased nutrient supply from riverine inflow, water column stratification and reduced oxygenation of bottom waters, and buffering of low bottom-water oxygen levels by accumulating terrestrial organic carbon.

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry (<1000m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500km from a coastline. Mean annual chlorophyll concentrations >2mgm−3 are only found within 50km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals.

Laminated sediments in the Bering Sea reveal atmospheric teleconnections to Greenland climate on millennial to decadal timescales during the last deglaciation

Abstract. During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin. We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bølling–Allerød and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling–Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and δ18O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions. We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1 mL L−1 and caused laminae preservation. Calculated benthic–planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bølling–Allerød and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730–990 yr during the Bølling–Allerød, 800–1100 yr in the Younger Dryas, and 765–775 yr for the Preboreal.

Global increase in export productivity during the Middle Eocene Climatic Optimum (MECO)?

Global increase in export productivity during the Middle Eocene Climatic Optimum (MECO)?

Changes in Southern Ocean bottom water environments associated with the Middle Eocene Climatic Optimum (MECO)

The Middle Eocene Climatic Optimum (MECO) was a ~650kyr long interval of pronounced warmth superimposed on the long-term Eocene cooling trend. We investigate benthic foraminiferal assemblage and fossil fish tooth cerium anomaly variability from Ocean Drilling Program (ODP) Site 738 in the Indian sector of the Southern Ocean (Southern Kerguelen Plateau) to assess changes in bottom water chemistry and effects on benthic foraminiferal ecosystems. The studied section spans 41.9 to 38.4Ma, encompassing the MECO as well as extensive Pre-MECO and Post-MECO intervals. We report a marked faunal turnover at 40.4Ma, 200kyrs after the onset of the MECO at ~40.6Ma, from an assemblage dominated by epifaunal benthic foraminifera to an infaunal-dominated assemblage. The infaunal domination persisted until the termination of the MECO at 39.95Ma. Thereafter, the Pre-MECO assemblage returned. This change is attributed to an increase in export productivity associated with the warming, possibly caused by an increase in continental runoff or the influence of a more eutrophic surface water mass. Superimposed on the change in tropic state the Ce/Ce* record shows a positive excursion during the 100kyrs long MECO peak warming at around 40.05Ma, indicative of a decrease in bottom-water oxygen content. Synchronously, infaunal benthic foraminifera drop briefly in abundance. Hence, we suggest that the peak warming is associated with bottom water oxygen depletion potentially caused by elevated productivity and/or a transient influence of an older, oxygen-depleted water mass.

Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

Abstract. The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene–Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ∼0.6 million year long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

Benthic foraminiferal assemblage turnover during intensification of the Northern Hemisphere glaciation in the Piacenzian Punta Piccola section (Southern Italy)

We present the results of a high-resolution analysis of the benthic foraminiferal assemblages at the Punta Piccola section (Stratotype for the Piacenzian Stage), which spans the gradual climate transition of the intensification of the Northern Hemisphere glaciation (3.6–2.6Ma). This study highlighted a major benthic foraminiferal fauna turnover, which started at about 3.05Ma with LO of Cibicidoides italicus, registered the gradual decline of Stilostomella spp. and culminated at about 2.7–2.75Ma, when the dominant Siphonina reticulata was replaced by Cibicidoides pachyderma, costate Bulimine, spinose Bulimine, spinose Uvigerine and the Bolivina dilatata group. Four compositional zones, identified by constrained cluster analysis, are indicative of palaeoenvironmental changes and document the transition from stable and mainly oligotrophic conditions to unstable, mesotrophic and more fluctuating bottom conditions.Two intervals of deposition of sapropelite clusters coded as O and A, investigated using both benthic and planktic assemblages, reveal that anoxia conditions were never reached. Planktic foraminifera in the sapropelite layers of cluster O indicate deep mixing and benthic foraminifera suggest an increase in export productivity to the sea floor. By contrast, planktic foraminifera in the uppermost sapropelite layers of cluster A indicate oligotrophic surface water conditions, stratification and more eutrophic subsurface water conditions, without deep mixing. The benthic foraminifera indicate hypoxic and eutrophic bottom conditions, and evidence the first episode of down-slope transport, which testifies to a strengthening of runoff and stratification of superficial waters, but not true stagnation.