Increased Marine Productivity Research Articles

Orbital (Hydro)Climate Variability in the Ice-Free Early Eocene Arctic.

Early Eocene (∼56-48Ma) climates are useful to investigate polar climate dynamics in the absence of ice. We explore early Eocene orbital variability of Arctic climate using sediments recovered by the Arctic Coring Expedition (ACEX). High resolution records of lipid biomarkers (GDGTs; 2-kyr) and palynological assemblages (5-kyr) in the ∼4m interval below Eocene Thermal Maximum 2 (∼54Ma) show cyclic signals related to ∼20-kyr precession, ∼40-kyr obliquity, and ∼100-kyr eccentricity. Biomarkers indicate obliquity and precession variability representative of sea surface temperature (SST) variations up to ∼1.4 and ∼0.5°C, respectively. Peak SSTs coincide with an elevated supply of pollen and spores and increased marine productivity. This implies an orbital control on precipitation and terrestrial nutrient supply to the Arctic Basin. Assuming that SST maxima correspond to Arctic insolation maxima (precession minima/obliquity maxima), precipitation maxima also correspond to insolation maxima, implying regional hydrological processes as a forcing rather than variations in meridional water transport, contrasting Pleistocene Arctic hydrology. The relative amplitudes of precession and obliquity in the SST record match that of local insolation between spring and fall, corroborating a seasonal GDGT bias. The reconstructed complete orbital imprint refutes a bias to one end of the orbital variability. Eccentricity-related SST variability was ∼0.8°C, ∼2-3 times higher than synchronous variability in the deep ocean, and 3-4 times higher than similar variations in the tropics. This confirms eccentricity-forced global temperature variability and that this had pronounced polar amplification, despite the absence of ice-albedo feedbacks.

Theory and classification of mass extinction causation.

Theory regarding the causation of mass extinctions is in need of systematization, which is the focus of this contribution. Every mass extinction has both an ultimate cause, i.e. the trigger that leads to various climato-environmental changes, and one or more proximate cause(s), i.e. the specific climato-environmental changes that result in elevated biotic mortality. With regard to ultimate causes, strong cases can be made that bolide (i.e. meteor) impacts, large igneous province (LIP) eruptions and bioevolutionary events have each triggered one or more of the Phanerozoic Big Five mass extinctions, and that tectono-oceanic changes have triggered some second-order extinction events. Apart from bolide impacts, other astronomical triggers (e.g. solar flares, gamma bursts and supernova explosions) remain entirely in the realm of speculation. With regard to proximate mechanisms, most extinctions are related to either carbon-release or carbon-burial processes, the former being associated with climatic warming, ocean acidification, reduced marine productivity and lower carbonate δ13C values, and the latter with climatic cooling, increased marine productivity and higher carbonate δ13C values. Environmental parameters such as marine redox conditions and terrestrial weathering intensity do not show consistent relationships with carbon-cycle changes. In this context, mass extinction causation can be usefully classified using a matrix of ultimate and proximate factors. Among the Big Five mass extinctions, the end-Cretaceous biocrisis is an example of a bolide-triggered carbon-release event, the end-Permian and end-Triassic biocrises are examples of LIP-triggered carbon-release events, and the Late Ordovician and Late Devonian biocrises are examples of bioevolution-triggered carbon-burial events. Whereas the bolide-impact and LIP-eruption mechanisms appear to invariably cause carbon release, bioevolutionary triggers can result in variable carbon-cycle changes, e.g. carbon burial during the Late Ordovician and Late Devonian events, carbon release associated with modern anthropogenic climate warming, and little to no carbon-cycle impact due to certain types of ecosystem change (e.g. the advent of the first predators around the end-Ediacaran; the appearance of Paleolithic human hunters in Australasia and the Americas). Broadly speaking, studies of mass extinction causation have suffered from insufficiently critical thinking-an impartial survey of the extant evidence shows that (i) hypotheses of a common ultimate cause (e.g. bolide impacts or LIP eruptions) for all Big Five mass extinctions are suspect given manifest differences in patterns of environmental and biotic change among them; (ii) the Late Ordovician and Late Devonian events were associated with carbon burial and long-term climatic cooling, i.e. changes that are inconsistent with a bolide-impact or LIP-eruption mechanism; and (iii) claims of periodicity in Phanerozoic mass extinctions depended critically on the now-disproven idea that they shared a common extrinsic trigger (i.e. bolide impacts).

Plio‐Pleistocene Ocean Circulation Changes in the Gulf of Alaska and Its Impacts on the Carbon and Nitrogen Cycles and the Cordilleran Ice Sheet Development

AbstractThe modern Gulf of Alaska (GOA) is a Cordilleran Ice Sheet (CIS) region, estimated to be important for nutrient cycling and CO2 exchange. Little is known of the GOA evolution over the Pliocene and Pleistocene as well as its impact on the CIS development, when other evidence for changing North Pacific circulation has emerged. We analyzed Integrated Ocean Drilling Program Expedition 341 Site U1417 sediments, which extend through the Plio‐Pleistocene transition (4–1.7 Ma), focusing on productivity‐related biomarkers (alkenones, brassicasterol), siliceous microfossils and bulk carbon and nitrogen stable isotopes. Our results show two dominant water column regimes: one characterized by high silica and low organic matter (OM) preservation, containing microorganism remains from a mix of habitats (4–3.7 Ma) and a second characterized by low biogenic silica and increased OM preservation of microorganisms from dominantly open ocean habitats (3.33–3.32 Ma and 2.8–1.66 Ma). An increase of phytoplankton diversity (3.7–3.35 Ma, 3.19–2.82 Ma) characterizes the two transitions of water column conditions, from oxygenated to reductive, that we attribute to a change from ocean mixing to strong stratified conditions with some occasional mixing. The biogeochemical changes in the GOA follow 400 and 100 kyr eccentricity cycles which are also reflected in changes in the CIS. We conclude that the CIS expansion created high nutrient low chlorophyll conditions in the GOA during the Mid Piacenzian Warm Period and the early Pleistocene. In turn, positive feedbacks increased marine productivity export, atmospheric CO2 drawdown and further CIS expansion.

Marine anoxia as a trigger for the largest Phanerozoic positive carbon isotope excursion: Evidence from carbonate barium isotope record

The mid-Ludfordian Lau carbon isotope excursion (Lau CIE) represents the largest positive carbon isotope excursion in the Phanerozoic (∼9‰), coincident with the biodiversity loss of many marine animal clades. Two main explanations for the Lau CIE are enhanced organic carbon burial via increased marine productivity and preservation-driven expansion of anoxia. While these two explanations are not mutually exclusive, the main driver of Lau CIE is yet to be constrained. Here, we resolve this longstanding debate using barium isotopes (δ138Ba) of marine carbonates deposited across the Lau CIE. Our δ138Ba data from the Kosov section (Czech Republic) record a large negative excursion in correlation to the positive shift in δ13Ccarb. We suggest that the observed negative shift in δ138Ba to values as low as −0.33‰ can be best interpreted as upwelling of isotopically light Ba from deeper waters due to pelagic barite dissolution under euxinic conditions. This hypothesis is consistent with results from barium concentration data as well as the results from the sulfate mass balance modeling that indicates a contraction in the seawater sulfate reservoir, with seawater sulfate concentrations decreasing from several mM ranges before the Lau CIE to less than 100 μM during Lau CIE. Taken together, evidence for a strong negative correlation between δ138Ba and δ13Ccarb suggests that shallow water anoxia, rather than enhanced marine productivity, was a primary driver of the Lau CIE that resulted in a notable decrease in the size of seawater sulfate reservoir.

Eocene-Oligocene paleoenvironmental changes in the South Orkney Microcontinent (Antarctica) linked to the opening of Powell Basin

The scarcity of paleo-records from the Antarctic Peninsular region of the Southern Ocean hinders our understanding of the timing of the opening of Drake Passage, specifically in the region of the South Orkney Microcontinent (SOM) and Powell Basin, between the Scotia and Antarctic plates. At Ocean Drilling Program (ODP) Hole 696B, SOM sediments recovered from the upper Eocene-lower Oligocene (~37.6–32.2 Ma) enable us to gain insight into paleoceanographic and paleoclimatic changes during gateway opening across the major Cenozoic climate shift —the Eocene-Oligocene transition— when the Antarctic ice sheet first reached sea-level. We propose the following sequence of events, based on a multi-proxy analysis of sediment facies, mineralogy, and organic matter geochemistry (TOC, TN, C/N ratio, δ 13 C, δ 15 N, and n -alkanes). During the late Eocene (~37.6–35.5 Ma) the SOM was attached to the Antarctic Peninsula, and terrigenous sediments of likely local origin were deposited in shallow waters under conditions of reduced‑oxygen/low-salinity, and temperate climate. In the latest Eocene (~35.5–34.1 Ma), terrigenous input was reduced due to the separation of the SOM from the Antarctic Peninsula by proto-Powell Basin opening. Decreased sediment supply during continuous deepening of the SOM led to deposition of a condensed section with significant glauconitization, recurrent winnowing by bottom currents, and suboxic conditions near the sediment-water interface. At the time of the Eocene-Oligocene transition (EOT; ~34.1–33.6 Ma) two upward-coarsening sediment sections were deposited within an overall upward-fining section, which we interpret as records of regressive phases due to ice sheet expansion. During the early Oligocene (~33.6–33.2 Ma) the SOM deepened further because of continued opening of Powell Basin, and organic-rich sediments were deposited as a result of enhanced biological production, partially driven by enhanced upwelling. Major cooling caused a change from forests indicating relatively humid temperate conditions in the late Eocene, to forests indicative of dry and cool conditions in the Oligocene, as shown by biomarker records, which also indicate weakening contributions of terrestrial organic matter to the marine sedimentary record. We thus conclude that a shallow gateway, the proto-Powell Basin, formed at ~35.5 Ma, as seen in the decreased delivery of proximal, coarse terrigenous sediments to the SOM margin; this was followed by a long-term deepening trend, interrupted by EOT regression due to continent-wide ice sheet build-up. Opening of the proto-Powell Basin could have provided a shallow-water pathway for water flowing from the Drake Passage-Scotia Sea towards the northern Weddell Sea, enhancing upwelling at the southern SOM shelf margin. Hence, increased marine productivity across the EOT might have resulted from the combined effects of the opening of Powell Basin and climate cooling. • Eocene-Oligocene sediments at Site 696 evidences a sustained relative sea-level rise in the SOM. • Our results point to the formation of the proto-Powell Basin at ~35.5 Ma. • Opening of Powell Basin provided a shallow-water pathway for water flowing towards the Weddell Sea. • We describe enhancing upwelling at the southern margin of the SOM shelf. • A shift from relatively humid temperate to dry and cool forests occurs between the Eocene and Oligocene.

Mid- to late-Holocene analysis of the influence of the La Plata River plume on the southwestern Atlantic shelf: A paleoenvironmental reconstruction based on lipid biomarkers and benthic foraminifera

A combined analysis of sedimentological, molecular, and microfossil proxies was used to determine paleoclimatic and paleoceanographic variations and assess sediment transport pathways along the last c.a. 6300 years in a sedimentary record collected on the inner shelf of the southwestern Atlantic Ocean. The combined use of terrestrial and marine proxies enables a more complete environmental perspective of the La Plata River plume influence on the southwestern Atlantic shelf, regarding the relationship between climate, productivity, as well as hydrodynamic. Variations in marine productivity, lipid biomarkers of terrestrial plants, diagnostic geochemical indices, and sea-surface temperature point to three phases within the core. The first interval (6300–5200 cal yr BP) was characterized by low marine and terrigenous organic matter input, with pulses of phytodetritus indicated by benthic foraminifera. These features suggested dry climatic conditions over the southeastern portion of South America, with the influence of sediments from the adjacent continent and, on a smaller scale, transported from the Argentinian shelf due to the high relative sea level. The second interval (5200–2800 cal yr BP) was distinguished by a slight increase in marine productivity and terrigenous input, indicating a transition period with an increase of total rainfall influenced by an intensified South American Monsoon System (SAMS) and the modern El Niño-Southern Oscillation (ENSO) phenomenon. These features, associated with the changes in wind patterns and the lower relative sea level, suggest the onset of the influence of the La Plata River (LPR) plume over the southern regions of the Brazilian continental shelf for the last 6300 cal yr BP. The last interval (2800–890 cal yr BP) had the highest contents of marine and terrigenous proxies, suggesting less climatic variability, as the long-term intensification of the SAMS and a further increase in the amplitude of the ENSO resulted in the modern establishment and dominant influence of the LPR plume on the core site. Variations in sea-surface temperature up to 3.3°C were related to the influence of the LPR plume on the shelf off southern Brazil.

Increased Marine Productivity in the Southern Humboldt Current System During MIS 2–4 and 10–11

AbstractThe Humboldt Current System (HCS) is characterized by high marine primary productivity, the dynamics of which are closely linked to climate variability. However, its changes beyond the last glacial cycle are virtually unknown due to a dearth of long sediment records. Here, we present a 500 ka multi‐proxy marine productivity reconstruction from the southernmost part of the HCS (∼43 S). At these latitudes, marine productivity changes have been typically attributed to glacial‐interglacial changes in the South Pacific Subtropical High (SPSH) and Southern Westerly Winds (SWWs). Surprisingly, our productivity reconstruction based on biomarkers and benthic foraminifera does not show recurrent glacial‐interglacial variability. Instead, large increases in organic matter flux occurred during MIS 2–4 and MIS 10–11. Micronutrients in aeolian dust and Southern Ocean‐sourced macronutrients seem to be unlikely drivers, as both would have led to recurrent glacial‐interglacial variability as observed elsewhere. Another source of micronutrients is via continental runoff, the amount of which is controlled by Patagonian Ice Sheet variability and/or precipitation. We interpret our productivity records as reflecting changes in the amount of nutrients supplied by continental runoff, which are driven by precipitation variations linked to the configuration of the SPSH‐SWWs in response to orbital forcing in the eccentricity band. During eccentricity minima, the position of SPSH changes minimally from precession minima to maxima. This SPSH‐SWWs configuration probably results in a prolonged period of high precipitation, which in turn increases the continental runoff and the supply of micronutrients to the sea.

Late Cenomanian-Turonian isotopic stratigraphy in the chalk of the Paris Basin (France): a reference section between the Tethyan and Boreal realms

A chemostratigraphic study (δ13C and δ18O) of the Late Cenomanian and Turonian chalk succession from the “Craie 701” Poigny borehole (near Provins in the Paris Basin, France) provides new high-resolution stable carbon and oxygen isotope data. Correlation of the bentonite horizons and the isotopic trends from Poigny with its English Chalk equivalent allows the development of a precise stratigraphic framework. δ13C and δ18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (a carbon isotope excursions: CIE of 3‰ amplitude) without any apparent anoxia in the Late Cenomanian Chalk. Comparisons between different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio Section, Italy) and the Vocontian Basin (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production, modulated by a regional effect on the organic carbon burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through to the Middle Turonian, including the salient CIE associated with the OAE 2, reflects a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can also be better defined by this isotopic study. A comparison of δ18O data between the Anglo-Paris Basin and Tethyan Basin shows high-amplitude, long-term synchronous variations reflecting primary paleo-environmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (−1‰ of amplitude) reflects a warmer climate regime, marking the onset of OAE 2. Two colder phases (+1‰ amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.

Calcareous nannofossil and foraminiferal trace element records in the Sorbas Basin: A new piece of the Messinian Salinity Crisis onset puzzle

The Messinian Salinity Crisis (MSC) was an extreme event that affected the Mediterranean Sea during the late Miocene, leading to massive evaporite deposition across the basin. Here we focus on the Perales section (Sorbas Basin, Western Mediterranean), using calcareous nannofossil (CN) and foraminiferal geochemical analyses to trace the paleoenvironmental dynamics culminating in the MSC onset. Orbital and tectonic forcing drove the CN fluctuations that correlated with the lithological quadripartite precessional cycle. Our integrated analysis reveals that cyclical sapropel deposition was triggered by an increase in marine productivity, followed by an increase in freshwater input and the development of a Deep Chlorophyll Maximum (DCM). The overlying marl records the protracted freshwater input that led to the shallowing of the DCM, decreasing organic carbon export and promoting seafloor re-oxygenation. Stratification, acting as a barrier, trapped part of the river-sourced nutrients below the photic zone. The subsequent gradual decrease in temperature promoted the disruption of the stratification, mixing nutrients upward into the photic zone and promoting diatom proliferation and preservation. When the reservoir of dissolved silica was exhausted, bioturbated marls were deposited at the top of the cycle. In the last pre-evaporitic cycle (UA34) the usual lithological cyclicity is obliterated; however the precessional footprint is revealed by CN fluctuations, suggesting that sapropel-like deposition lasted for most of the cycle. This cycle also records a succession of CN abundance peaks (MSC onset bioevent), as already recorded in several Mediterranean sections approximately at the MSC onset, suggesting that the same paleoenvironmental changes triggered the evaporitic phase in the whole Mediterranean. This bioevent marks the last step of water exchange reduction with the Atlantic (restriction pulse), which increased the sensitivity of the Mediterranean to freshwater input and associated nutrient delivery, culminating in a further increase in marine productivity.

Cretaceous oceanic anoxic events prolonged by phosphorus cycle feedbacks

Abstract. Oceanic anoxic events (OAEs) document major perturbations of the global carbon cycle with repercussions for the Earth's climate and ocean circulation that are relevant to understanding future climate trends. Here, we compare the onset and development of Cretaceous OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). OAE1a and OAE2 exhibit remarkable similarities in the evolution of their carbon isotope (δ13C) records, with long-lasting negative excursions preceding the onset of the main positive excursions, supporting the view that both OAEs were triggered by massive emissions of volcanic CO2 into the atmosphere. However, there are substantial differences, notably in the durations of individual phases within the δ13C positive excursions of both OAEs. Based on analysis of cyclic sediment variations, we estimate the duration of individual phases within OAE1a and OAE2. We identify (1) a precursor phase (negative excursion) lasting ∼430 kyr for OAE1a and ∼130 kyr for OAE2, (2) an onset phase of ∼390 and ∼70 kyr, (3) a peak phase of ∼600 and ∼90 kyr, (4) a plateau phase of ∼1340 and ∼200 kyr, and (5) a recovery phase of ∼380 and ∼440 kyr. The total duration of the positive δ13C excursion is estimated at 2700 kyr for OAE1a and 790 kyr for OAE2, and that of the main carbon accumulation phase is estimated at 980 and 180 kyr. The long-lasting peak, plateau and recovery phases imply fundamental changes in global nutrient cycles either (1) by submarine basalt–seawater interactions, (2) through excess nutrient inputs to the oceans by increasing continental weathering and river discharge, or (3) through nutrient recycling from the marine sediment reservoir. We investigated the role of phosphorus in the development of carbon accumulation by analysing phosphorus speciation across OAE2 and the mid-Cenomanian Event (MCE) in the Tarfaya Basin. The ratios of organic carbon and total nitrogen to reactive phosphorus (Corg∕Preact and Ntotal∕Preact) prior to OAE2 and the MCE hover close to or below the Redfield ratio characteristic of marine organic matter. Decreases in reactive phosphorus resulting in Corg∕Preact and Ntotal∕Preact above the Redfield ratio during the later phase of OAE2 and the MCE indicate leakage from the sedimentary column into the water column under the influence of intensified and expanded oxygen minimum zones. These results suggest that a positive feedback loop, rooted in the benthic phosphorus cycle, contributed to increased marine productivity and carbon burial over an extended period of time during OAEs.

Mesozoic C-cycle perturbations and climate: evidence for increased resilience of the Cretaceous biosphere to greenhouse pulses

The Mesozoic C-isotope record traces the history of the global carbon cycle. Major perturbations of the carbon cycle triggered by extraordinary volcanic activity are recorded in negative spikes coupled with positive C-isotope excursions. Prominent examples are the C-isotope anomaly events at the Permian–Triassic boundary and at the Triassic–Jurassic boundary, in the Toarcian or in the Aptian. While the major volcanic pulses at the Permian–Triassic and Triassic–Jurassic boundaries are considered as the main trigger of mass extinctions, carbon cycle perturbations in the Jurassic and Cretaceous were not accompanied by comparable extreme changes in marine or terrestrial biota. The data suggest either that changes in degassing of large igneous provinces explain the difference in the biota’s response to perturbation or (and) that the resilience of the Mesozoic biosphere to volcanic pulses changed through time. It is hypothesized that two factors contributed to the increased resilience of the biosphere in the Late Mesozoic: (1) starting in the Middle Jurassic, pelagic carbonate developed into an important sink of CO2in the long-term carbon cycle, contributing to increased resilience of the carbon cycle to perturbations, and (2) increasing fragmentation of Pangea resulted in the establishment of a transequatorial current system coupled with equatorial upwelling. This circulation pattern was intensified during greenhouse pulses. Increased marine productivity and widespread basinal anoxia favoured burial of organic carbon. Increased resilience of the Cretaceous biosphere against volcanic activity may explain why Deccan Trap volcanism was no longer sufficient as a trigger of a mass extinction at the Cretaceous–Paleogene boundary.

Chemostratigraphic resolution of widespread reducing conditions in the southwest Pacific Ocean during the Late Paleocene

Paleogene strata throughout much of the southwest Pacific is comprised of thick successions of fine-grained siliceous to calcareous sediments. However, during the Late Paleocene the south Pacific experienced widespread deposition of organic-rich and δ13Corg-enriched sediments that are recorded in the Waipawa Formation and the correlative Waipawa Organofacies. The mechanisms responsible for the elevated input and preservation of organic matter are still poorly understood. Using a multi-proxy chemostratigraphic approach we assess paleoceanographic conditions, including paleo-redox states and paleo-productivity of the Waipawa Formation. Eight key sections from the East Coast Basin, New Zealand were sampled and analysed for multi-element geochemistry and bulk pyrolysis. Sedimentological, stratigraphic and chemostratigraphic evidence indicates the south Pacific underwent an abrupt regression event during the Late Paleocene resulting in on-shelf erosion and/or bypassing of continental sourced sediments from the shelf into deeper waters. The change in sediment delivery further increased nutrients and terrestrial organic matter loading to the site of deposition. Coeval excursions in Ti/Zr and Rb/Sr indicate a shift to an aluminosilicate-dominated sediment supply, resulting in a modest increase in marine productivity that cannot account for the anomalous organic matter enrichment. Changes in the hydrogen index show a transition from terrestrial to mixed terrestrial–marine organic matter occurred during the Late Paleocene, in which high concentration of Type II-III kerogens were buried and preserved in association with enhanced water column reducing conditions in deep marine settings. Elevated concentrations of redox-sensitive trace elements (e.g. U, Mo, Fe, S) are consistent with alternating phases of dysoxic to oxic conditions suggesting an expansion of an oxygen minimum zone, enhancing preservation and delivery of organic matter to the seafloor, leading to the subsequent burial and preservation of organic matter within anoxic sediments. These new data provide insight into the depositional conditions and the petroleum potential of prospective source rocks in this basin using an integrated organic and inorganic geochemical approach to refine our knowledge of the depositional environment and paleoceanographic changes in shelfal to bathyal marine sediments of the Late Paleocene.

Intensified oceanic circulation during Early Carboniferous cooling events: Evidence from carbon and nitrogen isotopes

The Early Carboniferous was a climatic transition interval from a mid-Paleozoic greenhouse world into the Late Paleozoic Ice Age. It was marked by a long-term cooling trend that was punctuated by short glaciations in the Tournaisian and Visean (early to mid-Early Carboniferous). Here, we generated organic carbon and nitrogen isotope profiles for two widely separated Lower Carboniferous sections (Arrow Canyon Range, Nevada, and Namur-Dinant Basin, Belgium) in order to assess the global nature and timing of changes in the carbon‑nitrogen cycles linked to oceanic productivity and redox conditions during this climatic transition interval. The carbon and nitrogen isotope profiles of both study sections record major perturbations during the mid-Tournaisian and Visean. A mid-Tournaisian event (TICE) is marked by increases in δ13Ccarb, δ13Corg, and δ15Nbulk at Arrow Canyon (from +0.6 to +7.0‰, −25.2 to −23.7‰, and –0.6 to +8.9‰, respectively) and Namur-Dinant (from −0.3 to +4.7‰, −27.9‰ to −22.2‰, and –5.7 to +5.2‰, respectively). An early Visean event (VICE; named herein) is marked by increases in δ13Ccarb, δ13Corg, and δ15Nbulk at Arrow Canyon (from −0.6 to +3.1‰, −28.4 to −23.6‰, and +1.4 to +9.4‰, respectively) and Namur-Dinant (from +2.1 to +4.3‰, −26.7 to −25.0‰, and –1.4 to +3.3‰, respectively). The positive excursions in all three isotopic records during these events are consistent with increased fractional burial of organic carbon and enhanced denitrification, implying intensification of marine productivity and expansion of hypoxia in the global ocean. Given that each event coincided with lowering of sea-surface temperatures and increased glaciation (as documented from published conodont δ18O and sea-level records), we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins, triggering increased marine productivity and attendant redox changes within the affected upwelling zones. Our results provide new insights into changes in Early Carboniferous oceanic conditions in response to the initial stages of cooling leading into the Late Paleozoic Ice Age.

Late Pleistocene-Holocene coastal adaptation in central Mediterranean: Snapshots from Grotta d’Oriente (NW Sicily)

Marine faunal remains from Grotta d’Oriente (Favignana Island, NW Sicily) offer invaluable snapshots of human-coastal environment interaction in the central Mediterranean from the Late Pleistocene to the Middle Holocene. The long-term shellfish and fish records reflect human exploitation of coastal environments undergoing considerable reorganizations during the postglacial sea level rise and the progressive isolation of Favignana from mainland Sicily. We detected an intensification of marine resource exploitation between ∼9.6 ka and ∼7.8 ka BP, which corresponds with the isolation of Favignana Island and, later on, with the introduction of early agro-pastoral economy in this region. We suggest that a higher investment in marine resource exploitation by late foragers and early farmers in NW Sicily was also supported by an increase in marine productivity in the south Tyrrhenian Sea in the Middle Holocene.

Zn/Si records in diatom opal from Prydz Bay, East Antarctica

The Zn/Si records of diatom opal from Prydz Bay were investigated. The results show that the Zn/Si ratios range from 8 to 53μmolmol−1. The ratio from the continental slope is higher than those from the shelf. The difference in Zn/Si records could be attributed to the change of bioavailable Zn via the upwelling of Zn2+-rich deep water or the influence of oceanic water on the slope. However, phytoplankton productivity influences Zn/Si records on the continental shelf. Increased productivity leads to elevated Zn-pumping, and eventually to higher Zn/Si ratio in diatom opal. In this case, it is suggested that Zn/Si proxy could be a signal of marine productivity on the continental shelf of Prydz Bay. The down core profile of Zn/Si records shows an increase in marine productivity over the last century.

A multiproxy approach to the climate and marine productivity variations along MIS 5 in SE Brazil: A comparison between major components of calcareous nannofossil assemblages and geochemical records

In this study, changes in terrigenous input, based on geochemical elementary ratios (e.g. Fe/Ca, Ti/Ca, Ba/Ca, Fe/K), and on marine primary productivity, based on calcareous nannofossil assemblages, from the southeastern Brazilian continental margin are analyzed for the time interval 140 to 55ka (MIS 6 to MIS 4). Variation in the terrigenous input follows the continental paleoclimate records, based on speleothems from SE Brazil, and the summer insolation curve from low latitudes for the southern hemisphere. In turn, marine productivity shows a high correlation with terrigenous input. Terrigenous input maxima correlate to increased marine productivity during sub-stages 5d and 5b. Both, terrigenous input and marine productivity would be strongly controlled by changes in the Intertropical Convergence Zone and winds associated with the South Atlantic Convergence Zone. Thus, NE winds would have prevailed promoting humidity and precipitation rates over SE Brazil, as well as, an intensified wind-driven upwelling and eddies associated with the Brazil Current, which favored the presence of a shallow nutricline. Our results are consistent with that of different proxies presented in other studies providing estimates of changes on the precipitation rate of SE Brazil and changes on marine productivity in the South Atlantic Ocean during MIS 5.

North Pacific deglacial hypoxic events linked to abrupt ocean warming.

Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition. The mechanisms driving this hypoxia remain under debate. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4-5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals, and enhanced (15)N/(14)N ratio of organic matter, collectively suggest association with high export production. A decrease in (18)O/(16)O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming.

The consequences of opening the Sunda Strait on the hydrography of the eastern tropical Indian Ocean

AbstractThe advection of relatively fresh Java Sea water through the Sunda Strait is presently responsible for the low‐salinity “tongue” in the eastern tropical Indian Ocean with salinities as low as 32‰. The evolution of the hydrologic conditions in the eastern tropical Indian Ocean since the last glacial period, when the Sunda shelf was exposed and any advection via the Sunda Strait was cutoff, and the degree to which these conditions were affected by the Sunda Strait opening are not known. Here we have analyzed two sediment cores (GeoB 10042–1 and GeoB 10043–3) collected from the eastern tropical Indian Ocean off the Sunda Strait that cover the past ~40,000 years. We investigate the magnitude of terrigenous supply, sea surface temperature (SST), and seawater δ18O (δ18Osw) changes related to the sea level‐driven opening of the Sunda Strait. Our new spliced records off the Sunda Strait show that during the last glacial, average SST was cooler and δ18Osw was higher than elsewhere in the eastern tropical Indian Ocean. Seawater δ18O decreased ~0.5‰ after the opening of the Sunda Strait at ~10 kyr B.P. accompanied by an SST increase of 1.7°C. We suggest that fresher sea surface conditions have persisted ever since due to a continuous transport of low‐salinity Java Sea water into the eastern tropical Indian Ocean via the Sunda Strait that additionally increased marine productivity through the concomitant increase in terrigenous supply.

Flourishing ocean drives the end-Permian marine mass extinction

The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian-Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness.

Marine productivity leads organic matter preservation in sapropel S1: palynological evidence from a core east of the Nile River outflow

The formation of Eastern Mediterranean organic matter rich deposits known as sapropels is the results of two mechanisms: (enhanced) marine productivity and preservation of organic material at depth. However, their relative contribution and their leads and lags with respect to each other remain elusive. Here, we address these questions by studying sediments deposited prior to, during, and after the most recent sapropel (S1, ∼10–6 calibrated ka before present, BP) with an integrated marine and terrestrial palynological approach, combined with existing and newly generated geochemical data. The studied core was retrieved from an area under strong influence of the Nile outflow and has high average sediment accumulation rates allowing a high temporal resolution (of several decades to centuries).Marine productivity, as reconstructed with total dinocyst accumulation rates (ARs) and biogenic CaCO3 content, starts to increase ∼1ka prior to sapropel formation. A shift in the dinocyst taxa contributing to the productivity signal at sapropel onset indicates the rapid development of (seasonal) water column stratification. Pollen and spore ARs also increase prior to sapropel onset, but a few centuries after the increase in marine productivity. Hence, the first shift to a high marine productivity system before sapropel deposition may have been mostly favoured by the injection of nutrients via shoaling of the nutricline with a minor contribution of nutrients from land via river input and flooding of the shelves. Pollen assemblages indicate a gradual change across the sapropel onset from a savanna-like, through coastal marsh expansion, toward an open woodland assemblage, which is consistent with enhanced Nile influence and delta development. At sapropel onset a marked shift in pollen ARs could suggest increased preservation under anoxia. However, major shifts in pollen assemblages and signs of selective- or partial decomposition of terrestrial palynomorphs are absent. We therefore suggest that the high pollen ARs largely result from an increased influx of pollen by enhanced Nile discharge and extension of the freshwater plume. Three centuries after the sapropel onset, dinocyst ARs and CaCO3 content indicate that marine productivity starts to decrease, while sapropel deposition continued. Organic carbon content decreased only later and less dramatically. This may be explained by a shift in the dominance of the organisms contributing to marine productivity, to an enhanced preservation of organic matter, or a combination of both.