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1. New Foraminifera-Based Proxies to Trace Changes to the Organic and Inorganic Carbon System Since the Last Glacial Maximum.

   Fritz-Endres, Theresa (November 2021, Oregon State University)

   The production of carbon and export to deep ocean sediments is linked to carbon partitioning between the ocean and atmosphere and is a key driver of climate change over the glacial-interglacial transition. Yet conflicting reconstructions create barriers to understanding changes to the carbon system over this important climate transition. Production reconstructions conflict in part because commonly used production proxies may be subject to water column and seafloor diagenetic alterations that overprint primary oceanographic signals. In addition, reconstructions of deep ocean carbonate chemistry are complicated by the variable ways that dissolution/preservation affects the proxy. This dissertation explores the utility of new proxies recorded in the shells of planktic foraminifera that have the potential to reconstruct parameters of the carbon system and can be carefully assessed for signs of diagenesis. Proxy developments and reconstructions are made using foraminifera from equatorial Pacific Ocean sediments that span a gradient in surface ocean carbon production and deep ocean carbon preservation. 

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2. Volcanic Ash Deposition from Large Eruptions within the Last 150,000 Years Increases Biological Productivity in the Pacific Ocean at Low Latitudes

   Cruz, N; Martinez, V; Wu, J; Abbott, D (February 2024, Proceedings American Geophysical Union)

   Abbott, D (Ed.)

   Known as a bio-limiting metal, high abundances of iron in sea water can amplify biological productivity. The growth of diatoms and other photosynthetic organisms increases, providing more food for grazing organisms like foraminifera. The net result is more organic matter in surface waters and ultimately in surface sediments. Existing satellite data show increases in ocean chlorophyll in areas affected by volcanic eruptions. We infer from this that iron derived from volcanic ash does increase biological productivity. However, the relative increase in productivity is unknown. We examined 3 sediment cores from the Equatorial Western Pacific to analyze the relationship between volcanic ash and biological productivity: RC14-44, RC14-66, and RC14-67. All contain black or dark-colored foraminifera within ash layers and white-shelled foraminifera outside ash layers. We attribute the dark material outside and inside the foraminifera to organic carbon and metals. In our cores, some foraminifera are covered in iron sulfide (FeS), which could be pyrite, and contain large amounts of carbon as well as high abundances of aluminum and silicon. We examined barium concentrations to gain further knowledge of biological productivity at specific core depths as barium is a marker for primary productivity. We found that barium levels within ash layers increased at least ten-fold. Within ash layers, we also noticed that the ashes with higher amounts of fine silt and clay sized material have the greatest increase in barium content, perhaps related to explosion size. This pattern of increases in Ba, metals and organic carbon within ash layers compared to surrounding sediments shows that volcanic ash deposition increases marine productivity. For future research, measuring markers for biological productivity like biogenic silica content and loss on ignition (LOI) within and outside ash layers would further clarify the relationship between volcanic ash deposition and biological productivity. 

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3. Evidence for Increases in Biological Productivity from Deposition of Volcanic Ash near Low Latitude Volcanoes Located Outside the Gyres

   Abbott, D; Bostick, B; Wu, J; Cruz, N; Martinez, V (December 2023, Proceedings American Geophysical Union)

   Abbott, D (Ed.)

   Some satellite data show an increase in ocean chlorophyll in areas affected by volcanic eruptions. These increases in ocean color are thought to reflect an increase in photosynthetic activity by phytoplankton. These increases in primary production have been attributed to iron (Fe) from volcanic ash, particularly in high-latitude regions where primary productivity is limited by low Fe (the iron fertilization hypothesis). However, photosynthesis also appears to increase in the tropical ocean, for example in the Sunda and Ryukyu arcs and the Bismarck Sea, areas usually not thought to be iron limited. To examine the effects of volcanic ejecta on productivity in other areas, we examine relationships between ash deposition and biological productivity in three cores, RC14-44 (Sunda arc), VM28-309 (Ryukyu arc) and VM33-116 (Bismarck Sea). These cores contain volcanic ash layers with black or dark-colored foraminifera, different from the bright white foraminifera found outside of the ash layers. This dark coloration results primarily from organic carbon. In RC14-44, some foraminifera are coated with FeS and also contain high amounts of internal carbon. In VM28-309 and VM33-116, some foraminifera are filled with organic carbon rich materials, or have coatings rich in carbon. Occasionally, there are local enrichments in Fe within the foraminifera, indicative of extensive redox cycling. We attribute this carbon to increased biological productivity in these intervals. Barium (Ba) concentrations, a proxy for primary productivity because most or all Ba originates from organic matter contained in the sediment, is also enriched by up to 30-fold in the sediments containing ash. The ash layers with the highest amounts of fine material exhibit the largest enrichments in Ba, suggesting ash texture may influence the resulting changes in marine productivity. Overall, we find clear evidence that ash depositions increase both primary production and carbon export to sediments. Loss on ignition (LOI) and biogenic silica contents between and within ash layers, are potentially useful to further examine both the coupling between production and carbon burial, and the influence of ash deposition on phytoplankton community structure. 

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4. Increased Biological Productivity and Appearance of Black Foraminifera Due to Large Eruptions in the Past 150,000 Years at Low-Latitudes

   Martinez, V; Cruz, N; Abbott, D; Wu, J (February 2024, Proceedings American Geophysical Union)

   Abbott, D (Ed.)

   Volcanic eruptions deposit Fe-bearing volcanic ash in the ocean, thereby increasing biological productivity. The increased organic matter in areas of high biological productivity uses up oxygen as this organic matter decays and sinks through the water column. Past living beings, like foraminifera, ate organic matter that was carbon-rich and sometimes had metals absorbed into their carbon, creating coatings inside and outside their shells. These coatings can tell us about how biological productivity was affected before, during, and after the volcanic eruption. The studied cores are from the northwest Pacific Ocean and are close to geologically young volcanoes that are not well understood. The two cores that we focused on were VM28-309 and VM36-15 both taken by the Vema research ship. We studied the relationship between ash deposition and biological productivity by looking at all the ash layers in both cores. We found that in most of the ash layers, there were black or dark-colored foraminifera with coatings inside and outside the shells that were often carbon-rich and sometimes metal-rich. We attribute this coating to the increase of organic matter in surface waters when there was deposition of large amounts of volcanic ash. We also found high concentrations of Barium metal in VM28-309. Barium (Ba) is a biological marker because most or all Ba originates from the organic matter contained in sediments. We found that ash layers containing the finest materials (<38 micrometers in size) had the highest Ba content. For accurate results, we must sample above and below ash layers and select more sediment cores in the area. Also, Barium corrections must be done using data on biogenic silica contents. Loss on ignition (LOI) data will give us an estimate of the total organic carbon in each sample- allowing a second direct assessment of the increase in biological productivity produced by the deposition of volcanic ash. 

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5. Glacial‐interglacial changes in central tropical Pacific surface seawater property gradients

   https://doi.org/10.1002/2014PA002746  

   Lynch‐Stieglitz, Jean; Polissar, Pratigya J; Jacobel, Allison W; Hovan, Steven A; Pockalny, Robert A; Lyle, Mitchell; Murray, Richard W; Ravelo, A Christina; Bova, Samantha C; Dunlea, Ann G; et al (May 2015, Paleoceanography)

   Abstract Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminiferaGlobigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio ofG. ruberbetween the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific). 

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