More Like this

1. 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. 

   more » « less
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. 

   more » « less
3. Increased Productivity in the Equatorial Pacific During the Deglaciation Inferred From the Ba/Ca Ratios of Non‐Spinose Planktic Foraminifera

   https://doi.org/10.1029/2022PA004506  

   Fritz‐Endres, Theresa; Fehrenbacher, Jennifer S; Russell, Ann D; Cynar, Haley (December 2022, Paleoceanography and Paleoclimatology)

   Abstract The production and export of organic matter to deep‐sea sediments is a key driver in modulating glacial‐interglacial carbon cycles. Yet, it remains unsettled whether productivity has increased or decreased over glacial‐interglacial transitions, in part because productivity proxies may be complicated by sediment re‐deposition and diagenetic alterations. Here, we explore using non‐spinose foraminifera Ba/Ca ratios as a proxy for surface ocean productivity. We analyze foraminifera Ba/Ca ratios since the Last Glacial Maximum in cores that span a productivity gradient along the equatorial Pacific. Ba/Ca is low and invariable in the spinose speciesTrilobatus sacculifer. In contrast, Ba/Ca is higher and more variable in the non‐spinose speciesNeogloboquadrina dutertreiandPulleniatina obliquiloculata. Ba/Ca enrichment in non‐spinose species is hypothesized to be linked to the degradation of organic matter within the species' particulate microhabitat and reflects surface ocean particulate organic matter productivity at the time of shell calcification (Fehrenbacher et al., 2018,https://doi.org/10.1016/j.gca.2018.03.008). Ba/Ca in core‐top and sediment trap derived non‐spinose foraminifera correlate with organic matter productivity. We reconstruct an increase in non‐spinose species Ba/Ca during the deglacial in the western and eastern equatorial Pacific and suggest this may be linked to an increase in productivity, as observed in several other regional records. The 16–17 ka BP peak in non‐spinose foraminifera Ba/Ca is evident in specimens obtained from a deep ocean core and from regions that experience sediment focusing, suggesting the Ba/Ca proxy may be useful even in regions where samples are poorly preserved or complicated by sediment re‐deposition. 

   more » « less
4. Exploring the Toba Eruption: Impacts on Biological Productivity and Global Climate Dynamics

   Gairhe, Romin; Abbott, Dallas; Bostick, Benjamin (December 2024, American Geophysical Union)

   Our study examines how volcanic ash layers affect Earth's environment and climate, focusing on carbon, cadmium, and sulfur changes in deep-sea sediment from the Toba super eruption 74,000 years ago. This eruption, the largest of the Quaternary period, released 2,800 cubic kilometers of material and sulfur dioxide, which formed sulfate aerosols, potentially causing a volcanic winter. In sediment core RC14-37, we found a 15 cm thick Toba ash layer at 100-115 cm depth, with the highest ash concentration at 102-104 cm, significantly diluting the sulfur signal from 102-106 cm and masking the sulfur peak. Elevated sulfur levels just below the top of the ash layer suggest rapid deposition after most ash settled, with levels decreasing towards the base, indicating additional atmospheric sulfur. We used X-ray fluorescence (XRF) to measure sulfur and cadmium content. High cadmium levels in the ash layers suggest increased marine productivity. The SiO2 content in the ash ranged from 66% to 78%. Given that Toba ash contains 12 ppm sulfur, our corrected sulfur content (1700-3100 ppm) suggests most sulfur came from atmospheric sulfate aerosols. These results indicate increased biological productivity and sulfur in the ash layers, providing insights into the eruption's ecological impacts. 

   more » « less
5. Preferential Loss of High Trace Element Bearing Inner Calcite in Foraminifera During Physical and Chemical Cleaning

   https://doi.org/10.1029/2020GC009419  

   Fritz-enders, T; Fehrenbacher, J (December 2020, Geochemistry geophysics geosystems)

   null (Ed.)

   Plan language summary: Elements (including barium and magnesium) measured inside microscopic fossil shells are higher than expected and could reflect contamination or could reflect key information about the ancient surface ocean. For example, barium may reflect how much organic carbon is produced in the surface ocean, some of which is sunk to the deep ocean and thus removed from exchange with the atmosphere, effecting climate. Previous studies have attributed higher concentrations of these elements to contamination that forms on shells and have established harsh chemical cleaning techniques to remove the contamination. However, these cleaning techniques also remove parts of the shell that contain key information about past ocean conditions. We determine that high concentrations of these elements are not due to contamination in our samples and likely reflect conditions of the surface ocean. In future work, we suggest using techniques that measure at the microscale to confirm that there is no contamination and we suggest using more careful cleaning that preserves these elements. Preserving these elements in fossil shells may provide key information about organic carbon production and cycling in the surface ocean, which is critical to reconstruct carbon exchange between the atmosphere and ocean. 

   more » « less