Iván Hernández-Almeida

Last Name

Hernández-Almeida

First Name

Iván

ORCID

0000-0002-9329-8357

Organisational unit

09601 - Stoll, Heather / Stoll, Heather

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Publications1 - 10 of 34

Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years
Weber, Michael E.; Bailey, Ian; Hemming, Sidney R.; et al. (2022)
Nature Communications
The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels.
Carbon Isotopic Fractionation of Alkenones and Gephyrocapsa Coccoliths Over the Late Quaternary (Marine Isotope Stages 12–9) Glacial-Interglacial Cycles at the Western Tropical Atlantic
González-Lanchas, Alba; Hernández-Almeida, Iván; Flores, José A.; et al. (2021)
Paleoceanography and Paleoclimatology
The sensitivity of coccolithophores to changing CO2 and its role modulating cellular photosynthetic carbon isotopic fractionation (εp) is crucial to understand the future adaptation of these organisms to higher CO2 world and to assess the reliability of εp for past CO2 estimation. Here, we present εp measured on natural fossil samples across the glacial-interglacial (G-I) CO2 variations of marine isotope stages 12 to 9 interval (454–334 ka) at the western tropical Atlantic Ocean Drilling Program Site 925 together with a set of organic and inorganic geochemical, micropaleontological and morphometrical data from Gephyrocapsa coccoliths in the same samples. The ∼2‰ variation in εp is significantly correlated with the CO2[aq] concentrations calculated from assumption of air-sea equilibrium with measured ice core pCO2 concentrations. The sensitivity of εp to CO2[aq] is similar to that derived from a multiple regression model of culture observations and is not well simulated with the classical purely diffusive model of algal CO2 acquisition. The measured range of Gephyrocapsa cell sizes is insufficient to explain the non-CO2 effects on εp at this location, via either direct size effect or growth rate correlated to cell size. Primary productivity, potentially triggered by shifting growth rates and light levels, may also affect εp. Proposed productivity proxies % Florisphaera profunda and the ratio between the C37 to C38.et alkenone (C37/C38.et ratio) both correlates modestly with the non-CO2 effects on εp. When the observed G-I εp to CO2 sensitivity at this site is used to estimate pCO2 from εp since the Miocene, the inferred pCO2 declines are larger in amplitude compared to that calculated from a theoretical εp diffusive model. We find that oxygen and carbon stable isotope vital effects in the near monogeneric-separated Gephyrocapsa coccoliths (respectively Δδ18OGephyrocapsa–Trilobatus sacculifer and εcoccolith) are coupled through the time series, but the origins of these vital effects are not readily explained by existing models.
Latitudinal Variance in the Drivers and Pacing of Warmth During Mid-Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean
Warnock, Jonathan P.; Reilly, Brendan T.; Raymo, Maureen E.; et al. (2022)
Paleoceanography and Paleoclimatology
Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000-year resolution, spanning 1.110–1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59°S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacial.
The source of Pleistocene carbonate below the CCD in the central basin of South China Sea: Evidences from coccolith and geochemistry
Zhang, Hongrui; Zhou, Xinquan; Jiang, Xiaoying; et al. (2023)
Marine Geology
Carbonate dissolution and deposition in the deep ocean is a critical component of carbon cycle, but detailed pictures of carbonate dynamics below the Carbonate Compensation Depth (CCD) remains poorly understood. In this study, we present a ∼ 420 thousand years record of carbonate content below CCD in IODP Site U1433 at 4.4 km water depth in the South China Sea (SCS). Instead of carbonate-free sediment, we observed that the carbonate content in this deep site could reach as high as 40%. The dissolution-resistant biogenic carbonate, coccoliths, and stable isotope ratio of bulk carbonate were analyzed to trace the carbonate sources. The coccolith assemblage in IODP Site U1433 shows an unrealistic feature of high productivity, which indicates a lateral transport of coccoliths from the northern SCS to the central basin. Coccoliths' contribution to total carbonate was on average 30% and could be as high as ∼80%. Their contribution to carbonate increased at the expense of the dissolution of other biogenic carbonate, such as foraminifera, and decreased with the dilution of other terrestrial carbonate particles. According to the thickness of coccoliths, significant dissolution of coccoliths only happened when the carbonate content dropped below 3%. Marbles from Taiwan, with negative oxygen isotope ratios, and early diagenetic carbonates from carbonate platform nearby, with both negative carbon and oxygen isotope ratios, could be the other important sources besides the marine biogenic carbonate. With help of numerical simulations, we estimated that the lateral transport by turbidity currents could contribute up to 70–90% of the deep-sea sediment in the central basin of SCS. These new findings enrich our knowledge of the carbon fluxes from continental margins to the deep ocean as a key part of the carbon cycle.
Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry
Gerotto, Amanda; Zhang, Hongrui; Nagai, Renata Hanae; et al. (2023)
Biogeosciences
Understanding the variations in past ocean carbonate chemistry is critical to elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complex physiological and ecological response to the carbonate system during an organisms' life cycle and the potential for preservation at the seafloor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi > 2 μm, and small Gephyrocapsa spp.). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks) of coccoliths in a laboratory dissolution experiment and surface sediment samples from the South China Sea. The coccolith morphological data in surface sediments were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicates that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs. length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain the main variations observed in our work. We propose that the normalized ks variation (σ/ks), which is the ratio between the standard deviation of ks (σ) and the mean ks, could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. Applied together with the σ/ks ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.
Clumped isotopes in globally distributed Holocene coccoliths reveal their habitat depth
Mejía, Luz M.; Bernasconi, Stefano M.; Zhang, Hongrui; et al. (2023)
Earth and Planetary Science Letters
Reliable temperature reconstructions are necessary to improve climate reconstructions and comparisons with paleoclimate model simulations. Most existing paleotemperature proxies are based on organic and inorganic remains of marine organisms. Despite the evidence that the habitat depth of coccolithophores and other phytoplankton depend on their ability to balance light, nutrients, and grazing pressure, calibrations of proxies based on photosynthesizers often assume they live in the surface ocean. Here we present the first globally distributed dataset of core top multi-species coccolith clumped isotopes (Δ47), which show a clear latitudinal thermal gradient and demonstrate coccolith Δ47 sensitivity to temperature. The application of the most recent Δ47-temperature calibration for marine biogenic carbonates yields calcification temperatures implying deep habitats of ∼50 to ∼150 m for tropical coccolithophores, which could photosynthesize with 1-10% of surface photosynthetic active radiation (PAR) levels. Because of the uncertainties of Δ47 thermometry and of the low upper ocean temperature gradient, at well-mixed high-latitude locations, coccolith Δ47 cannot be used to reliably constrain a specific habitat depth. Nevertheless, Δ47 is a good indicator of paleotemperatures of the mixed layer. We also use coccolith Δ47 to derive the first regression relating core top coccolith Δ47 and sea surface temperatures (SST). Although this formulation cannot be considered a proper coccolith-specific Δ47 calibration, since it ignores coccolithophore's potential for calcification at depth, it facilitates comparison with temperature proxies like U37k′, which are regressed to SST, rather than production temperature.
A new radiolarian transfer function for the Pacific Ocean and application to fossil records: Assessing potential and limitations for the last glacial-interglacial cycle
Hernández-Almeida, Iván; Boltovskoy, Demetrio; Kruglikova, Svetlana B.; et al. (2020)
Global and Planetary Change
The FORCIS database: A global census of planktonic Foraminifera from ocean waters
Chaabane, Sonia; de Garidel-Thoron, Thibault; Giraud, Xavier; et al. (2023)
Scientific Data
Planktonic Foraminifera are unique paleo-environmental indicators through their excellent fossil record in ocean sediments. Their distribution and diversity are affected by different environmental factors including anthropogenically forced ocean and climate change. Until now, historical changes in their distribution have not been fully assessed at the global scale. Here we present the FORCIS (Foraminifera Response to Climatic Stress) database on foraminiferal species diversity and distribution in the global ocean from 1910 until 2018 including published and unpublished data. The FORCIS database includes data collected using plankton tows, continuous plankton recorder, sediment traps and plankton pump, and contains similar to 22,000, similar to 157,000, similar to 9,000, similar to 400 subsamples, respectively (one single plankton aliquot collected within a depth range, time interval, size fraction range, at a single location) from each category. Our database provides a perspective of the distribution patterns of planktonic Foraminifera in the global ocean on large spatial (regional to basin scale, and at the vertical scale), and temporal (seasonal to interdecadal) scales over the past century.
Nonlinear increase in seawater ⁸⁷Sr ∕ ⁸⁶Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering
Stoll, Heather; Pena, Leopoldo D.; Hernández-Almeida, Iván; et al. (2024)
Climate of the Past
The ⁸⁷Sr / ⁸⁶Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and the mid-Oligocene to mid-Miocene period features the most rapid rates of increase in the ⁸⁷Sr / ⁸⁶Sr of the Cenozoic. Because previous records of the ⁸⁷Sr / ⁸⁶Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambiguously distinguish million-year-scale variations in the rate of ⁸⁷Sr / ⁸⁶Sr change from variations in sedimentation rate. In this study, we produce the first ⁸⁷Sr / ⁸⁶Sr results from an Oligocene to early Miocene site with a precise age-model-derived orbital tuning of high-resolution benthic δ¹⁸O at Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in ⁸⁷Sr / ⁸⁶Sr, as well as periods of relative stasis. These changes can be directly compared with the high-resolution benthic δ¹⁸O at the same site. We find that slowing of the rate of ⁸⁷Sr / ⁸⁶Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the mid-Oligocene glacial interval, and a rapid steeping in the ⁸⁷Sr / ⁸⁶Sr increase coincides with the benthic δ¹⁸O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctica. We additionally generate the first ⁸⁷Sr / ⁸⁶Sr data from ODP Site 1168 on the Tasman Rise and Integrated Ocean Drilling Program (IODP) Site 1406 of the Newfoundland Margin during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere midlatitude sites and to better estimate the duration of early Miocene hiatus and condensed sedimentation.
Shallower Living Depth Instead of Higher Seawater Alkalinity Enhanced Calcification in Bloom‐Forming Coccolithophores During Their Pleistocene Acme Event
Zhang, Hongrui; Wijker, Reto; Hernández-Almeida, Iván; et al. (2025)
AGU Advances
Coccolithophores are a group of marine phytoplankton precipitating about 50% of total calcite carbonate in the surface ocean. During the Pleistocene, coccolithophores experienced several periodic high-abundance and dominance intervals (acmes) that significantly altered the ocean carbon cycle by increasing the production of carbonate in the ocean. However, the reason for these episodes of enhanced calcification is still unclear. Here, we focus on one of the most significant dominance intervals, the Gephyrocapsa caribbeanica acme event, that lasted between ∼500 and 300 thousand years ago. We find that the variations of seawater alkalinity made only a minor contribution to the increased calcification rates during coccolithophore blooms. Rather, coccolithophore carbon isotopic fractionation indicates that coccolithophores employed a stronger bicarbonate pumping to increase intracellular carbon availability. Greater nutrient availability and shallower living depth likely facilitated higher bicarbonate pumping rates. The upregulation of bicarbonate pumping indicates the vital role of nutrients and light, and not only the ocean carbonate system, in the evolution of marine phytoplankton. Models of future coccolithophore calcification response to changing ocean carbon chemistry would, therefore, benefit from a more comprehensive consideration of how light and nutrient availability affect cellular energy budgets and drive carbon uptake.

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Iván Hernández-Almeida

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