The Mg/Ca of planktic foraminifera Globigerinoides ruber (white) is a widely applied proxy for tropical and sub-tropical sea-surface temperature. The accuracy with which temperature can be ...reconstructed depends on how accurately relationships between Mg/Ca and temperature and the multiple secondary controls on Mg/Ca are known; however, these relationships remain poorly quantified under oceanic conditions. Here, we present new calibrations based on 440 sediment trap/plankton tow samples from the Atlantic, Pacific and Indian Oceans, including 130 new samples from the Bay of Bengal/Arabian Sea and the tropical Atlantic Ocean. Our results indicate temperature, salinity and the carbonate system all significantly influence Mg/Ca in G. ruber (white). We propose two calibration models: The first model assumes pH is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.0±0.8%/°C (2σ), a salinity sensitivity of 3.3±2.2%/PSU and a pH sensitivity of −8.3±7.7%/0.1 pH units; The second model assumes carbonate ion concentration (CO32−) is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.7±0.8%/°C, a salinity sensitivity of 5.0±3.0%/PSU and a CO32− sensitivity of −0.24±0.11%/μmol kg−1. In both models, the temperature sensitivity is significantly lower than the widely-applied sensitivity of 9.0±0.6%/°C. Application of our new calibrations to down-core data from the Last Glacial Maximum, considering whole ocean changes in salinity and carbonate chemistry, indicate a cooling of 2.4±1.6°C in the tropical oceans if pH is the controlling parameter and 1.5±1.4°C if CO32− is the controlling parameter.
•New Mg/Ca calibration based on 440 sediment trap/plankton tow samples.•The sensitivity of Mg/Ca to temperature is ∼6/°C.•The sensitivity of Mg/Ca to salinity is ∼3%.•The carbonate system significantly influences Mg/Ca.
We have compiled the first stratigraphically continuous high‐resolution benthic foraminiferal stable isotope record for the Paleocene from a single site utilizing cores recovered at Pacific ODP Site ...1209. The long‐term trend in the benthic isotope record suggests a close coupling of volcanic CO2 input and deep‐sea warming. Over the short‐term the record is characterized by slow excursions with a pronounced periodic beat related to the short (100 kyr) and long (405 kyr) eccentricity cycle. The phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the Oligocene and Miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on Milankovitch time scales. In addition, the record documents an unusual transient warming of 2°C coeval with a 0.6‰ carbon isotope excursion and a decrease in carbonate content at 61.75 Ma. This event, which bears some resemblance to Eocene hyperthermals, marks the onset of a long‐term decline in δ13C. The timing indicates it might be related to the initiation of volcanism along Greenland margin.
Key Points
High‐resolution benthic foraminiferal stable isotope record for Paleocene Pacific
On the short term, orbital forcing is the pace maker for Paleocene paleoclimate
On the long term, close coupling of volcanic CO2 input and deep sea warming
Millennial-scale Atlantic meridional overturning circulation (AMOC) variability has often been invoked to explain the Dansgaard–Oeschger (DO) events. However, the underlying causes responsible for ...millennial-scale AMOC variability are still debated. High-resolution U37K′ and TEX86H temperature records for the last 50kyr obtained from the tropical Northeast (NE) Atlantic (core GeoB7926-2, 20°13′N, 18°27′W, 2500m water depth) show that distinctive DO-type subsurface (i.e. below the mixed layer: >20m water depth) temperature oscillations occurred with amplitudes of up to 8°C in the tropical NE Atlantic during Marine Isotope Stage 3 (MIS3). Statistical analyses reveal a positive relationship between the reconstructed substantial cooling of subsurface waters and prominent surface warming over Greenland during DO interstadials. General circulation model (GCM) simulations without external freshwater forcing, the mechanism often invoked in explaining DO events, demonstrate similar anti-phase correlations between AMOC and pronounced NE Atlantic subsurface temperatures under glacial climate conditions. Together with our paleoproxy dataset, this suggests that the vertical temperature structure and associated changes in AMOC were key elements governing DO events during the last glacial.
► We present two temperature records from the tropical Atlantic for the last 50kyr. ► Our records show distinctive DO-type subsurface temperature oscillations. ► Statistical analyses reveal a cooling of subsurface waters during DO interstadials. ► We modeled without external freshwater forcing under the glacial condition. ► Our model simulations show similar anti-phase behavior.
We combine stable isotope, calcareous nannoplankton, and benthic foraminiferal records for Ocean Drilling Program Sites 1262 (paleodepth ~3,500 m) and 1263 (paleodepth ~1,500 m) on Walvis Ridge (SE ...Atlantic), to document the marine biotic response to Eocene Thermal Maximum 3, in the early part of the Early Eocene Climate Optimum, ~3.1 Myr after the Paleocene/Eocene Thermal Maximum. Bottom water warming may have decreased the vertical thermal gradient at both sites, but more at Site 1263 than at Site 1262. Floral and faunal changes were more muted at Site 1262 than at shallower Site 1263, indicating that carbonate dissolution was not the most important cause of biotic effects. Assemblage changes were more pronounced in benthos than in plankton. Calcareous nannofossils underwent minor ecological changes, possibly related to the presence of warmer waters, especially at Site 1263, and dissolution‐resistant taxa increased in abundance. Benthic foraminiferal diversity decreased at both sites, but benthic foraminiferal accumulation rates declined dramatically at Site 1263, remaining stable at Site 1262. Ocean circulation may have changed during ETM3, resulting in the presence of a warmer (intermediate) water mass at Site 1263. More pronounced warming may have caused enhanced remineralization of organic matter, so less food reached the benthos. The biotic response to the X‐event was less pronounced than that to earlier and more severe hyperthermal events, the Paleocene/Eocene Thermal Maximum and Eocene Thermal Maximum 2. The extent of the biotic response reflects the severity of the environmental disturbance but varies by location (e.g., paleodepth on Walvis Ridge).
Plain Language Summary
We can learn about the effects of future global warming on oceanic life forms by studying records of global warming episodes in the past. We studied a global warming episode ~52.8 million years ago, when the world was much warmer than today (e.g., no ice sheets on Antarctica). We used samples collected by the International Ocean Discovery Program through deep‐sea drilling in the Southeast Atlantic, at two sites (~1,500 and ~3,500‐m water depth at the time of the events). We investigated calcareous, microscopic fossils formed by one‐celled, plant‐like organisms (photosynthesizers) floating in the upper waters and microscopic fossils of one‐celled animal‐like organisms, which lived on and in mud on the seafloor. We analyzed their shells chemically, using that information to reconstruct water temperatures. We noted that seafloor organisms suffered more change during the global warming than surface dwellers, especially at the shallower site, where waters warmed more than at greater depth. The effects on life forms were mainly caused by the warming itself, which influences how much food the organisms need, so that organisms in the warmest waters were relatively starved. We compared our data with those on other periods of global warming and concluded that more severe warming generally resulted in more severe effects on ocean life.
Key Points
We reconstruct ecological and environmental changes across Eocene Thermal Maximum 3 in the SE Atlantic
Stable isotope and microfossil analysis shows that warming and ecological change were more marked at intermediate than at greater depth
Circulation changes and/or greater relative warming at high latitudes could have produced this pattern
Planktic foraminiferal flux data from time-series sediment trap observations have been compiled from 42 sites across the world's oceans, comprising a variety of oceanographic settings. To analyze ...species sensitivity to environmental parameters, distributional and optimum ranges are derived by relating fluxes and relative abundances of the following seven species to sea surface temperature (SST) and export production normalized to 1000 m water depth:
Globigerinoides ruber (white and pink),
G. sacculifer,
Globigerinella siphonifera,
Globigerina bulloides and
Neogloboquadrina pachyderma (dextral and sinistral coiling varieties).
Of the warm-water species,
G. ruber (white) and
G. sacculifer exhibit the widest SST tolerance range (9.7/9.8–31°C), followed by
G. siphonifera (11.9–31°C), while
G. ruber (pink) shows the narrowest SST range (16.4–29.6°C).
G. bulloides and
N. pachyderma (dex.) cover almost the whole SST range,
N. pachyderma (dex.) exhibiting a clear preference for mid-temperatures, while the distribution pattern of
G. bulloides is polymodal due to different genetic types comprised in this morphologically defined category. The polar–subpolar species
N. pachyderma (sin.) is absent at SSTs above 23.7°C. The change in dominance of right- over left-coiled
N. pachyderma is observed at 9°C. Derived optimum ranges for all species are in good agreement with previous plankton tow and laboratory studies, while lower temperature limits for
G. ruber (white) and
G. sacculifer might be several degrees lower than previously reported. With the exception of the morphospecies
G. bulloides, SST has a significant effect on all investigated species. However, it seems to be a governing factor for species fluxes only at the edges of the thermal tolerance range.
The influence of export production on planktic foraminiferal fluxes and relative abundances is not as pronounced. Highest relative abundances of the symbiont-bearing and thus light-dependent species
G. ruber,
G. sacculifer and
G. siphonifera are restricted to oligotrophic and mesotrophic conditions, even though high fluxes can be observed at high export productions as well. In contrast, the asymbiotic species
G. bulloides and
N. pachyderma (dex.), depending more on food, reach high fluxes and relative abundances even at very high rates of export production, where they can easily outnumber the symbiotic species. Within the joint space of both SST and export production,
N. pachyderma (sin.) yielded high fluxes and relative abundances coinciding mostly with medium to high export productivities.
Eastern Boundary Upwelling Ecosystems (EBUEs) are associated with high biological productivity, high fish catch and they highly contribute to marine carbon sequestration. Whether coastal upwelling ...has intensified or weakened under climate change in the past decades is controversially discussed and different approaches (e.g., time-series of chlorophyll, wind, sea surface temperature, modeling experiments) have been considered. We present a record of almost two decades of particle fluxes (1991–2009) from ca. 600 to 3100 m water depth in the Canary Basin at site ESTOC (European Station for Time series in the Ocean Canary Islands; ca. 29°N, 15°30.W, ca. 3600 m water depth), located in the offshore transition zone of the northern Canary Current-EBUE. We compare these flux records with those measured at a mesotrophic sediment trap site further south off Cape Blanc (Mauritania, ca. 21°N). The deep ocean fluxes at ESTOC in ca. 3 km recorded the evolution of the coastal Cape Ghir filament (30–32°N, 10–12°W) due to lateral advection of particles, whereas the upper water column sediment traps in ca. 1 km reflected the oligotrophic conditions in the overlying waters of ESTOC. We observed an increased emphasis in spring-time fluxes since 2005, associated with a change in particle composition, while satellite chlorophyll biomass did not show this pattern. Due to its northern location in the CC-EBUEs, spring biogenic fluxes at ESTOC provide a better relationship to the forcing of the North Atlantic Oscillation than those recorded further south off Cape Blanc. Off Cape Blanc, deep fluxes showed the best overlap with the deep ESTOC fluxes during the spring season before 2005. On the long-term, both chlorophyll and particle fluxes showed an increasing trend at ESTOC which was not observed further south at the mesotrophic Cape Blanc site. This might indicate that, depending on their location along the NW African margin, coastal upwelling systems react differently to global change.
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