About

Michael A. McCarthy is a critical social theorist and political sociologist at the University of California, Santa Cruz. His work focuses on addressing the complex challenges posed by finance capitalism, including its role in worsening social inequality, deepening poverty, increasing macroeconomic instability, and accelerating climate degradation. Through his scholarship, activism, and policy design, McCarthy seeks to develop democratic processes for investing that prioritize social and environmental well-being. He advocates for rebuilding systems of investment and debt allocation by creating institutions that enhance economic democracy. His research and collaborations span topics such as democratic finance, economic populism, and the political philosophy of liberalism, reflecting a commitment to integrating critical social theory with practical solutions for economic and environmental justice.

Research topics

• Biology
• Environmental science
• Geology
• Environmental chemistry
• Oceanography
• Ecology
• Chemistry
• Paleontology
• Mineralogy
• Biochemistry
• Chromatography
• Organic chemistry

Selected publications

• Comment on egusphere-2026-2228

  2026-05-24

  peer-reviewOpen access

  <strong class="journal-contentHeaderColor">Abstract.</strong> Planktic foraminifera form shells that are preserved in ocean sediments and are used in a variety of paleoproxy and biostratigraphic applications. However, species-specific ecology can complicate the interpretation of planktic foraminifera-based proxies, and limited options exist for examining the ecology of extinct species. Here we apply test-bound compound-specific stable isotopes of amino acids (CSI-AA) to examine the trophic ecology of extant planktic foraminifera. We measure CSI-AA in planktic foraminifera shells collected in sediment traps from the Santa Barbara Basin, CA, specifically the three most abundant species in this region: <em>Globigerina bulloides</em>, <em>Neogloboquadrina incompta</em>, and <em>Turborotalita quinqueloba</em>. The nitrogen CSI-AA of all three species suggest that planktic foraminifera have metazoan-like metabolisms, and that trophic position estimates using CSI-AA are appropriate for planktic foraminifera. All three species had trophic positions near 2 (primary consumer), with no evidence for mixotrophy or photosymbionts. Carbon CSI-AA, in combination with a Bayesian stable isotope mixing model, indicates that the three species occupied separate niches based on diet. <em>Globigerina bulloides</em> fed opportunistically on all groups of phytoplankton available in Santa Barbara Basin, adjusting its diet with seasonal changes in phytoplankton assemblage. <em>Turborotalita quinqueloba</em> specialized in diatoms and heterotrophic bacteria. <em>Neogloboquadrina incompta</em> consumed heterotrophic bacteria and some phytoplankton. Our results align with the current understanding of each species&rsquo; ecology while further defining their niches. Our findings suggest that CSI-AA is a promising tool for understanding the trophic ecology of planktic foraminifera, and we make recommendations for future applications of CSI-AA to fossil specimens.

  PublisherDOI

• Ground-truthing the application of compound-specific stable isotopes of amino acids to planktic foraminifera tests from Santa Barbara Basin

  2026-04-23

  articleOpen access

  Abstract. Planktic foraminifera form shells that are preserved in ocean sediments and are used in a variety of paleoproxy and biostratigraphic applications. However, species-specific ecology can complicate the interpretation of planktic foraminifera-based proxies, and limited options exist for examining the ecology of extinct species. Here we apply test-bound compound-specific stable isotopes of amino acids (CSI-AA) to examine the trophic ecology of extant planktic foraminifera. We measure CSI-AA in planktic foraminifera shells collected in sediment traps from the Santa Barbara Basin, CA, specifically the three most abundant species in this region: Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba. The nitrogen CSI-AA of all three species suggest that planktic foraminifera have metazoan-like metabolisms, and that trophic position estimates using CSI-AA are appropriate for planktic foraminifera. All three species had trophic positions near 2 (primary consumer), with no evidence for mixotrophy or photosymbionts. Carbon CSI-AA, in combination with a Bayesian stable isotope mixing model, indicates that the three species occupied separate niches based on diet. Globigerina bulloides fed opportunistically on all groups of phytoplankton available in Santa Barbara Basin, adjusting its diet with seasonal changes in phytoplankton assemblage. Turborotalita quinqueloba specialized in diatoms and heterotrophic bacteria. Neogloboquadrina incompta consumed heterotrophic bacteria and some phytoplankton. Our results align with the current understanding of each species’ ecology while further defining their niches. Our findings suggest that CSI-AA is a promising tool for understanding the trophic ecology of planktic foraminifera, and we make recommendations for future applications of CSI-AA to fossil specimens.

  PublisherOA PDFDOI

• Organic and isotopic indicators for sorting of sedimentary organic matter along a marginal submarine canyon

  Geochimica et Cosmochimica Acta · 2026-03-19

  article
  PublisherDOI

• Proteinaceous deep sea coral amino acid isotope records reveal climate-driven decadal-scale planktic ecosystem fluctuations

  Geochimica et Cosmochimica Acta · 2025-02-15 · 2 citations

  articleOpen accessSenior author

  Decadal-scale climate variability drives important fluctuations in nutrient availability and productivity in highly productive eastern boundary current upwelling ecosystems, but the relatively brief duration of most monitoring efforts limits understanding of these dynamics. When applied to high-resolution paleoarchives such as deep-sea proteinaceous coral skeletons, stable carbon and nitrogen isotope (δ 13 C and δ 15 N) analysis can provide useful new insight into biogeochemical and ecological changes beyond the instrumental record. However, interpretation of bulk δ 13 C and δ 15 N records is often complicated by multiple possible drivers of variability. Here, we addressed these challenges by applying both bulk and compound-specific amino acid δ 15 N and δ 13 C analysis to two bamboo coral specimens from Sur Ridge on the central California margin, generating sub-decadal resolution records spanning c. 1810 to present. Our overarching goals were to first test amino acid δ 13 C and δ 15 N proxies in proteinaceous deep-sea bamboo coral archives, and second to investigate links between climate forcing and biogeochemical responses on the California margin over the Anthropocene. Together, comparison of deep-sea coral amino acid trophic position results to local sediment traps and endmember mixing analysis indicate that bamboo coral feed directly on exported sinking particles, which are comprised primarily of zooplankton fecal pellets (>70 %). This new evidence contradicts some past work based on bulk δ 15 N analysis alone and validates bamboo coral as archives of euphotic zone processes. Amino acid δ 15 N proxies also reveal that trophic position, not baseline δ 15 N of nitrate or phytoplankton production, is the primary driver of bulk δ 15 N variability in these coral records from a highly-productive coastal upwelling environment. Our approximately 200-year reconstruction shows overall long-term ecosystem stability since the pre-industrial period, overlain by major multidecadal-scale fluctuations in bamboo coral trophic position and δ 13 C of primary production. Relatively high (low) trophic position and low (high) δ 13 C values of primary production occurred during negative (positive) phases of the Pacific Decadal Oscillation over the 20th century. Counter to expectations, these results suggest lower primary production likely occurred during past periods of high nitrate availability in our study region. Modern satellite chlorophyll-a observations corroborate this finding. We hypothesize that offshore transport and subduction of nutrients and phytoplankton and/or precipitation-mediated changes in iron availability may link climate variability and planktic ecosystem dynamics in this region.

  PublisherDOI

• Special delivery of proteinaceous matter to deep-sea microbes

  Science Advances · 2025-03-19 · 11 citations

  articleOpen accessSenior author

  Earth's deep ocean holds a vast reservoir of dissolved organic carbon, traditionally considered old and resistant to microbial degradation. Radiocarbon analyses indicate the hidden occurrence of younger dissolved organic carbon components, assumed to be accessible to deep-sea microorganisms but not yet demonstrated. Using compound-class radiocarbon analysis, molecular characterization, and bioassay experiments, we provide direct evidence for rapid microbial utilization of young, labile, high-molecular weight proteinaceous material in bathypelagic waters. The abundance of labile proteinaceous material diminishes from epipelagic to mesopelagic waters but notably increases in bathypelagic waters, where it exhibits a short turnover time (days) and resembles surface plankton in molecular composition. This observation coincides with peak zooplankton biomass recorded over the year. The nonmonotonic depth trend suggests a deep-sea replenishment of organic particles from mesopelagic migrating zooplankton. Our results indicate the presence of labile organic molecules at bathypelagic depths and reveal a nonlinear supply of plankton-derived substrates that support microbial metabolism and carbon sequestration in the deep ocean.

  PublisherDOI

• Improved solid-state 13C and 15N NMR reveals fundamental compositional divide between refractory dissolved organic carbon and nitrogen in the sea

  Geochimica et Cosmochimica Acta · 2024-09-20 · 4 citations

  articleOpen accessSenior author

  Marine dissolved organic matter (DOM) is one of the largest reservoirs of organic carbon and nitrogen in the world. Yet, despite its global importance, most DOM remains molecularly uncharacterized. Solid-state nuclear magnetic resonance (NMR) spectroscopy of isolated DOM fractions represents one of the most powerful techniques to understand overall structural composition . However, it is well known that standard cross polarization magic angle spinning (CP/MAS) NMR, the technique used for almost all past solid-state NMR studies of DOM, is at best “semi-quantitative,” and underestimates fully substituted NMR active nuclei. Additionally, almost all past solid-state NMR work analyzed high molecular weight (HMW) material isolated by ultrafiltration , which is now understood to represent mostly 14 C-young, “semi-labile” compounds. In contrast, there is far less information regarding the composition of older, low molecular weight (LMW) DOM, which represents the vast majority of the ocean’s accumulated refractory DOM pool. Here, we applied 13 C and 15 N solid-state multiCP/MAS NMR, improved NMR methods optimized to more quantitatively resolve fully substituted NMR nuclei , to both HMW and LMW DOM isolated from the surface and deep North Pacific Subtropical Gyre. These methods confirm past work indicating most nitrogen containing HMW DOM as amide compounds, but also demonstrate a modest heterocyclic N component not previously identified. In contrast, we found that LMW DON is almost entirely aromatic heterocyclic N, consistent with the hypothesis that heterocyclic N structures may be largely responsible for the accumulation of the ocean’s refractory DON pool. Surprisingly, however, we find DOC aromatic functionalities still represent only a very minor portion of either the HMW or the LMW refractory carbon pools, in marked contrast to refractory DON composition. Together, these more quantitative solid-state NMR techniques likely represent the most accurate picture of DON and DOC functional and compound-class makeup to date, and so have broad implications for our understanding of marine DOM structure and cycling. Specifically, our new data suggests that while chemical composition likely acts as a key control on DOM lability, the most refractory components of DOC and DON have very different compositions, sources, and cycling, supporting the idea that DOC and DON cycling in the ocean may be largely decoupled.

  PublisherDOI

• Tropical decadal variability in nutrient supply and phytoplankton community in the Central Equatorial Pacific during the late Holocene

  Scientific Reports · 2024-02-20 · 1 citations

  articleOpen accessSenior author

  Abstract We have reconstructed baseline δ 15 N and δ 13 C of export production at Kingman Reef in the Central Equatorial Pacific (CEP) at sub-decadal resolution, nearly continuously over the last 2000 years. The changes in δ 15 N reflects the strength of the North Equatorial Counter Current (NECC) relative to the South Equatorial Current (SEC), and to a lesser extent, the North Equatorial Current (NEC). Seasonal to multi-decadal variation in the strength of these currents, through the redistribution of heat, have global climate impacts and influence marine and terrestrial ecosystems. We use modern El Niño-La Nina dynamics and the Tropical Pacific Decadal Variability (TPDV) pattern, which is defined in the CEP, as a framework for analyzing the isotopic data. The CEP δ 15 N and δ 13 C records exhibit multi-decadal (50–60 year) variability consistent with TPDV. A large multi-centennial feature in the CEP δ 15 N data, within age-model uncertainties, is consistent with one of the prolonged dry-pluvial sequences in the American west at the end of the Medieval Climate Anomaly, where low TPDV is correlated with drier conditions. This unique record shows that the strength of the NECC, as reflected in baseline δ 15 N and δ 13 C, has at quasi-predictable intervals throughout the late Holocene, toggled the phytoplankton community between prokaryotes and picoplankton versus eukaryotes.

  PublisherOA PDFDOI

• Capturing How the Accelerometer Measured Physical Activity Profile Differs in People with Diabetic Foot Ulceration

  Sensors · 2024-07-27 · 2 citations

  articleOpen access

  Diabetic Foot Ulcers (DFUs) are a major complication of diabetes, with treatment requiring offloading. This study aimed to capture how the accelerometer-assessed physical activity profile differs in those with DFUs compared to those with diabetes but without ulceration (non-DFU). Participants were requested to wear an accelerometer on their non-dominant wrist for up to 8days. Physical activity outcomes included average acceleration (volume), intensity gradient (intensity distribution), the intensity of the most active sustained (continuous) 5–120 min of activity (MXCONT), and accumulated 5–120 min of activity (MXACC). A total of 595 participants (non-DFU = 561, DFU = 34) were included in the analysis. Average acceleration was lower in DFU participants compared to non-DFU participants (21.9 mg [95%CI:21.2, 22.7] vs. 16.9 mg [15.3, 18.8], p &lt; 0.001). DFU participants also had a lower intensity gradient, indicating proportionally less time spent in higher-intensity activities. The relative difference between DFU and non-DFU participants was greater for sustained activity (MXCONT) than for accumulated (MXACC) activity. In conclusion, physical activity, particularly the intensity of sustained activity, is lower in those with DFUs compared to non-DFUs. This highlights the need for safe, offloaded modes of activity that contribute to an active lifestyle for people with DFUs.

  PublisherOA PDFDOI

• Physical and biogeochemical drivers of multi-year isoscape in the California upwelling system

  Scientific Reports · 2024-12-28 · 5 citations

  articleOpen accessSenior author

  Stable isotopes of carbon (δ13C) and nitrogen (δ15N) are commonly employed to reconstruct past change in marine ecosystems and nutrient cycling. However, multiple biogeochemical and physical drivers govern spatiotemporal variability of these isotopic signals, particularly in dynamic coastal systems, complicating interpretation. Here, we coupled a modern multi-year (2010–2019) δ13C and δ15N isoscape record from intertidal mussels (Mytilus californianus) with high-resolution ocean model output and satellite chlorophyll-a observations in the California Current System (32°–43° N) to identify major drivers of isotopic variability. Our results show that spatial variations in δ13C are largely related to primary production, whereas spatial δ15N variability is driven by water mass mixing. Major isotopic change was also related to ocean climate variability; however, these effects vary regionally. In northern and central California, δ15N values are predominantly a function of nitrate utilization, whereas in southern California, δ15N varies due to shifts in water mass composition. In all regions, δ13C values are driven by productivity, with the largest changes occurring in southern California. Our findings provide novel insight into regional differences in predominant drivers of isotopic variability, and links to modern ocean climate variability. These findings offer crucial information needed for robust interpretations of California Current palaeoceanographic δ13C and δ15N records.

  PublisherOA PDFDOI

• Variable aging and storage of dissolved black carbon in the ocean

  Proceedings of the National Academy of Sciences · 2024-03-22 · 21 citations

  articleOpen access

  During wildfires and fossil fuel combustion, biomass is converted to black carbon (BC) via incomplete combustion. BC enters the ocean by rivers and atmospheric deposition contributing to the marine dissolved organic carbon (DOC) pool. The fate of BC is considered to reside in the marine DOC pool, where the oldest BC 14 C ages have been measured (&gt;20,000 14 C y), implying long-term storage. DOC is the largest exchangeable pool of organic carbon in the oceans, yet most DOC (&gt;80%) remains molecularly uncharacterized. Here, we report 14 C measurements on size-fractionated dissolved BC (DBC) obtained using benzene polycarboxylic acids as molecular tracers to constrain the sources and cycling of DBC and its contributions to refractory DOC (RDOC) in a site in the North Pacific Ocean. Our results reveal that the cycling of DBC is more dynamic and heterogeneous than previously believed though it does not comprise a single, uniformly “old” 14 C age. Instead, both semilabile and refractory DBC components are distributed among size fractions of DOC. We report that DBC cycles within DOC as a component of RDOC, exhibiting turnover in the ocean on millennia timescales. DBC within the low-molecular-weight DOC pool is large, environmentally persistent and constitutes the size fraction that is responsible for long-term DBC storage. We speculate that sea surface processes, including bacterial remineralization (via the coupling of photooxidation of surface DBC and bacterial co-metabolism), sorption onto sinking particles and surface photochemical oxidation, modify DBC composition and turnover, ultimately controlling the fate of DBC and RDOC in the ocean.

  PublisherOA PDFDOI

Recent grants

• The Microobial Nitrogen Pump: Coupling 14C and Compound-specific Amino Acids to Understand the Role of Microbial Transformations in the Refractory Ocean DON Pool

  NSF · $600k · 2014–2018

• The Use of Nitrogen Isotopes of Amino Acids To Understand Marine Sedimentary 15N Records

  NSF · $350k · 2011–2016

Frequent coauthors

• Ana Christina Ravelo

  University of California, Santa Cruz

  67 shared

• Melanie J. Davies

  NIHR Leicester Biomedical Research Centre

  57 shared

• Petra Dekens

  55 shared

• T. P. Guilderson

  55 shared

• Marcelo Barreiro

  Universidad de la República

  49 shared

• А. В. Федоров

  49 shared

• S. George Philander

  Princeton University

  49 shared

• Peter B deMenocal

  Lamont-Doherty Earth Observatory

  42 shared

Awards & honors

• Paul Sweezy Award
• Honorable Mention for the Labor and Labor Movements Award