Alfredo Martínez-García

Alfredo Martínez-García
Max Planck Institute for Chemistry | mpic · Department of Climate Geochemistry

Doctor of Philosophy

About

181
Publications
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Publications

Publications (181)
Article
Incorporation of animal-based foods into early hominin diets has been hypothesized to be a major catalyst of many important evolutionary events, including brain expansion. However, direct evidence of the onset and evolution of animal resource consumption in hominins remains elusive. The nitrogen-15 to nitrogen-14 ratio of collagen provides trophic...
Article
The impact of global warming on the ocean’s oxygen-deficient zones (ODZs) is uncertain, partly because of a lack of data on past changes. We report monthly resolved records of coral skeleton–bound nitrogen isotopes (CS-δ ¹⁵ N) to reconstruct denitrification in the Eastern Tropical North Pacific (ETNP) ODZ over the last 80 years. The data indicate s...
Article
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Rationale Compound‐specific stable isotope analysis of hydrogen (δD) and carbon (δ ¹³ C) in organic compounds is a valuable tool in biogeochemical research. A key limitation of this method is the relatively large amount of sample required to achieve desirable precision. Methods We developed a large‐volume (20 μL) injection method that allows for h...
Article
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Previous studies have reported an accumulation of nitrous oxide (N2O) on shallow continental shelves of the western Arctic Ocean. In this study, we sampled seawater profiles for N2O measurements in the eastern Arctic shelves, in the North Kara Sea, in the context of the Arctic Century Expedition. Despite some variability in the vertical distributio...
Article
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The ability of stony corals to thrive in the oligotrophic (low-nutrient, low-productivity) surface waters of the tropical ocean is commonly attributed to their symbiotic relationship with photosynthetic dinoflagellates1,2. The evolutionary history of this symbiosis might clarify its organismal and environmental roles³, but its prevalence through ti...
Article
Full-text available
Seawater transported into the South Atlantic from the Indian Ocean via “Agulhas leakage” modulates global ocean circulation and has been linked to glacial‐interglacial climate cycles. However, constraining past Agulhas leakage has been a challenge. We sampled a transect of the Cape Basin in winter 2017 that intersected a mature Agulhas eddy and fou...
Article
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The 72‐foot sailing yacht Eugen Seibold is a new research platform for contamination‐free sampling of the water column and atmosphere for biological, chemical, and physical properties, and the exchange processes between the two realms. Ultimate goal of the project is a better understanding of the modern and past ocean and climate. Operations starte...
Article
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N2 fixation in low‐latitude surface waters dominates the input of fixed nitrogen (N) to the global ocean, sustaining ocean fertility. In the Caribbean Sea, higher foraminifera‐bound (FB‐)δ¹⁵N indicates a decline in N2 fixation during ice ages, but its cause and broader implications are unclear. Here, we report three additional Atlantic FB‐δ¹⁵N reco...
Preprint
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Foraminifera often form symbiotic relationships with photosynthetic algae, providing a host environment and inorganic nutrients in exchange for photosynthetic organic matter from the algal symbiont. To date, the history of this relationship has been studied in paleoceanographic records with the oxygen and carbon stable isotopes of foraminiferal cal...
Article
The nitrogen isotopes of the organic matter preserved in fossil fish otoliths (ear stones) are a promising tool for reconstructing past environmental changes. We analyzed the ¹⁵ N/ ¹⁴ N ratio (δ ¹⁵ N) of fossil otolith-bound organic matter in Late Cretaceous fish otoliths (of Eutawichthys maastrichtiensis , Eutawichthys zideki and Pterothrissus sp....
Poster
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The ca. 0.7 Ma old Thomas Quarry I - Grotte à Hominidés (ThI-GH) in Casablanca (Morocco) has yielded well-preserved faunal remains (including Homo sp.) as well as Acheulean artefacts, offering a unique opportunity to study the environment and ecology of the earliest hominins in Morocco. The ThI-GH faunal assemblage is taxonomically diverse, compris...
Article
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Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these re...
Article
Zinc (Zn) is vital to marine organisms. Its active uptake by phytoplankton results in a substantial depletion of dissolved Zn, and Zn bound to particulate organic matter replenishes dissolved Zn in the ocean through remineralization. However, we found that particulate Zn changes from Zn bound to phosphoryls in cells to recalcitrant inorganic pools...
Article
Full-text available
Millennial-scale climate variations during the last glacial period, such as Dansgaard–Oeschger (DO) cycles and Heinrich events, have been extensively studied using ice core and marine proxy records. However, there is a limited understanding of the magnitude of these temperature fluctuations in continental regions, and questions remain about the sea...
Article
Full-text available
The Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability1–3. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity⁴. Whereas palaeoceanographic reconstructions exhibit regional heterogen...
Article
Full-text available
Terrestrial glacial records from the Patagonian Andes and New Zealand Alps document quasi-synchronous Southern Hemisphere–wide glacier advances during the late Quaternary. However, these records are inherently incomplete. Here, we provide a continuous marine record of western–central Patagonian ice sheet (PIS) extent over a complete glacial–intergl...
Article
The global ocean’s oxygen inventory is declining in response to global warming, but the future of the low-oxygen tropics is uncertain. We report new evidence for tropical oxygenation during the Paleocene-Eocene Thermal Maximum (PETM), a warming event that serves as a geologic analog to anthropogenic warming. Foraminifera-bound nitrogen isotopes ind...
Article
Full-text available
Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial cycl...
Article
The nitrogen isotopic composition ( ¹⁵ N/ ¹⁴ N ratio, or δ ¹⁵ N) of enameloid‐bound organic matter (δ ¹⁵ N EB ) in shark teeth was recently developed to investigate the biogeochemistry and trophic structures (i.e., food webs) of the ancient ocean. Using δ ¹⁵ N EB , we present the first nitrogen isotopic evidence for trophic differences between shar...
Preprint
Full-text available
A growing body of observations reveals rapid changes in both the total inventory and distribution of marine oxygen over the later half of the 21st century, leading to increased interest in extending oxygenation records into the past. Use of paleo-oxygen proxies have the potential to extend the spatial and temporal range of current records, bound pr...
Article
Full-text available
Seabirds transfer nutrients from the ocean to their nesting island, potentially altering nitrogen (N) cycling within adjacent terrestrial and marine ecosystems. Yet, the processes involved in seabird‐N transfer along the land–sea continuum remain elusive. Using δ ¹⁵ N and δ ¹⁸ O measurements of groundwater nitrate, we demonstrate the role of bracki...
Article
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The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB‐δ ¹⁵ N) using the oxidation–denitrifier (O–D) method provides a novel tool to study past changes in N cycling processes. Methods We report a set of methodological improvements to the O–D method, including (a) a method for sealing the r...
Article
Full-text available
Most anthropogenic nitrogen (N) reaches coastal waters via rivers carrying increasing loads of sewage, fertilizer, and sediments. To understand anthropogenic N impacts, we need to understand historical N-dynamics before human influence. Stable isotope ratios of N preserved in carbonates are one way to create temporal N records. However, records tha...
Article
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Studies have suggested that cancerous tissue has a lower ¹⁵N/¹⁴N ratio than benign tissue. However, human data have been inconclusive, possibly due to constraints on experimental design. Here, we used high-sensitivity nitrogen isotope methods to assess the ¹⁵N/¹⁴N ratio of human breast, lung, and kidney cancer tissue at unprecedented spatial resolu...
Preprint
Seawater transported into the South Atlantic from the Indian Ocean via “Agulhas leakage” modulates global ocean circulation and has been linked to glacial-interglacial climate cycles. However, constraining past Agulhas leakage remains a challenge. Using new measurements from the modern South Atlantic, we propose that the δ15N of organic matter pres...
Conference Paper
Nitrogen isotopes of enameloid-bound organic matter (δ15NEB) in fossil shark teeth offer unique insight into their trophic ecology. Traditionally, tooth morphology and preserved evidence of predator-prey interactions are used to infer the feeding behavior of sharks in the fossil record. Here, we apply the δ15NEB proxy to two species of Lamniformes...
Preprint
Full-text available
Millennial-scale climate variations during the last glacial period, such as Dansgaard–Oeschger (D/O) cycles and Heinrich events, have been extensively studied using ice core and marine proxy records. However, there is a limited understanding of the magnitude of these temperature fluctuations in continental regions, and questions remain about the se...
Article
Full-text available
There is limited understanding of temperature and atmospheric circulation changes that accompany an Atlantic Meridional Overturning Circulation (AMOC) slowdown beyond the North Atlantic realm. A Peqi'in Cave (Israel) speleothem dated to the last interglacial period (LIG), 129-116 thousand years ago (ka), together with a large modern rainfall monito...
Preprint
Full-text available
The ability of scleractinian corals to thrive in the oligotrophic (low-nutrient, low-productivity) surface waters of the tropical ocean is commonly attributed to their symbiotic relationship with photosynthetic dinoflagellates 1,2 . The evolutionary history of this symbiosis might clarify its organismal and environmental roles. It is currently uncl...
Article
Full-text available
The oxygen content of the oceans is susceptible to climate change and has declined in recent decades¹, with the largest effect in oxygen-deficient zones (ODZs)², that is, mid-depth ocean regions with oxygen concentrations <5 μmol kg⁻¹ (ref. ³). Earth-system-model simulations of climate warming predict that ODZs will expand until at least 2100. The...
Article
Full-text available
Nitrogen isotopes are widely used to study the trophic position of animals in modern food webs; however, their application in the fossil record is severely limited by degradation of organic material during fossilization. In this study, we show that the nitrogen isotope composition of organic matter preserved in mammalian tooth enamel (δ¹⁵Nenamel) r...
Article
Full-text available
The greater Agulhas Current region is an important component of the climate system, yet its influence on carbon and nutrient cycling is poorly understood. Here, we use nitrate isotopes (δ¹⁵N, δ¹⁸O, Δ(15–18) = δ¹⁵N–δ¹⁸O) to trace regional water mass circulation and investigate nitrogen cycling in the Agulhas Current and adjacent recirculating waters...
Article
Full-text available
It is understood that the global mean ocean nitrate δ¹⁵N is set by the δ¹⁵N of the input of fixed nitrogen (N) to the ocean (mostly N2 fixation) and the net isotopic discrimination of fixed N loss (mostly denitrification). Here, we demonstrate that, in addition to the fixed nitrogen input/output budget, the isotopic discrimination of nitrate assimi...
Article
Full-text available
The proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) candidate site of West Flower Garden Bank (27.8762°N, 93.8147°W) is an open ocean location in the Gulf of Mexico with a submerged coral reef and few direct human impacts. Corals contain highly accurate and precise (<±1 year) internal chronologies, similar to tree rings, a...
Article
Full-text available
Corals are unique in the suite of proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) archives, as living organisms that produce aragonite exoskeletons preserved in the geological record that contain highly accurate and precise (<±1 year) internal chronologies. The GSSP candidate site North Flinders Reef in the Coral Sea (Aust...
Article
Corals are unique in the suite of proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) archives, as living organisms that produce aragonite exoskeletons preserved in the geological record that contain highly accurate and precise (<±1 year) internal chronologies. The GSSP candidate site North Flinders Reef in the Coral Sea (Aust...
Article
Full-text available
Along the coastal Tropical Eastern Pacific (TEP), regions of strong seasonal upwelling bring cold, nutrient-rich waters, controlling ecological conditions and sustaining millions of people through large-scale fisheries. The TEP is also important for the regulation of global climate and is affected by large-scale environmental processes such as ENSO...
Article
The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60...
Article
Full-text available
The analyses of the stable isotope ratios of carbon (δ¹³C), nitrogen (δ¹⁵N), and oxygen (δ¹⁸O) in animal tissues are powerful tools for reconstructing the feeding behavior of individual animals and characterizing trophic interactions in food webs. Of these biomaterials, tooth enamel is the hardest, most mineralized vertebrate tissue and therefore l...
Article
Full-text available
Lake sediment records from Holzmaar and the infilled maar of Auel (Eifel, Germany) are used to reconstruct landscape changes and megafauna abundances. Our data document a forested landscape from 60,000 to 48,000 yr b2k and a stepwise vegetation change towards a glacial desert after 26,000 yr b2k. The Eifel landscape was continuously inhabited from...
Article
Full-text available
The modern Pacific Ocean hosts the largest oxygen-deficient zones (ODZs), where oxygen concentrations are so low that nitrate is used to respire organic matter. The history of the ODZs may offer key insights into ocean deoxygenation under future global warming. In a 12-My record from the southeastern Pacific, we observe a >10‰increase in foraminife...
Article
Full-text available
Dissolved oxygen (O 2 ) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming 1,2 . However, models provide an unclear picture of future ODZ c...
Article
Full-text available
Fossil-bound organic material holds great potential for the reconstruction of past changes in nitrogen (N) cycling. Here, with a series of laboratory experiments, we assess the potential effect of oxidative degradation, fossil dissolution, and thermal alteration on the fossil-bound N isotopic composition of different fossil types, including deep an...
Preprint
Full-text available
Nitrogen isotopes are widely used to study the trophic position of animals in modern food webs, however, their application in the fossil record is severely limited by degradation of organic material during fossilization. In this study, we show that the nitrogen isotopic composition of organic matter preserved in mammalian tooth enamel (δ15Nenamel)...
Article
Full-text available
Trophic position is a fundamental characteristic of animals, yet it is unknown in many extinct species. In this study, we ground-truth the 15N/14N ratio of enameloid-bound organic matter (δ15NEB) as a trophic level proxy by comparison to dentin collagen δ15N and apply this method to the fossil record to reconstruct the trophic level of the megatoot...
Preprint
Full-text available
The Southern Hemisphere Westerly Winds (SWW) drive upwelling south of the Antarctic Polar Front (PF) that vents CO2 to the atmosphere. During the ice ages, a northward (equatorward) shift of the PF may have reduced this CO2 venting, helping to explain the lower atmospheric CO2 concentration of those times. However, evidence of PF migration is lacki...
Article
Full-text available
During glacial terminations, massive iceberg discharges and meltwater pulses in the North Atlantic triggered a shutdown of the Atlantic Meridional Overturning Circulation (AMOC). Speleothem calcium carbonate oxygen isotope records (δ ¹⁸ O Cc ) indicate that the collapse of the AMOC caused dramatic changes in the distribution and variability of the...