The Impacts of Flood, Drought, and Turbidites on Organic Carbon Burial Over the Past 2,000 years in the Santa Barbara Basin, California

Climate conditions and instantaneous depositional events can influence the relative contribution of sediments from terrestrial and marine environments and ultimately the quantity and composition of carbon buried in the sediment record. Here, we analyze the elemental, isotopic, and organic geochemical composition of marine sediments to identify terrestrial and marine sources in sediment horizons associated with droughts, turbidites, and floods in the Santa Barbara Basin (SBB), California, during the last 2,000 years. Stable isotopes (δ13C and δ15N) indicate that more terrestrial organic carbon (OC) was deposited during floods relative to background sediment, while bulk C to nitrogen (C/N) ratios remained relatively constant (~10). Long- chain n- alkanes (C27, C29, C31, and C33), characteristic of terrestrial OC, dominated all types of sediment deposition but were 4 times more abundant in flood layers. Marine algae (C15, C17, and C19) and macrophytes (C21 and C23) were also 2 times higher in flood versus background sediments. Turbidites contained twice the terrestrial n- alkanes relative to background sediment. Conversely, drought intervals were only distinguishable from background sediment by their higher proportion of marine algal n- alkanes. Combined, our data indicate that 15% of the total OC buried in SBB over the past 2,000 years was deposited during 11 flood events where the sediment was mostly terrestrially derived, and another 12% of deep sediment OC burial was derived from shelf remobilization during six turbidite events. Relative to twentieth century river runoff, our data suggest that floods result in considerable terrestrial OC burial on the continental margins of California.Key PointsTerrestrial organic carbon is the dominant source of carbon to the SBB with deposition significantly increasing during flood eventsEpisodic flood and turbidite remobilization events were responsible for over 25% of the OC buried in the SBB over the past 2,000 yearsDrought sedimentation had significantly lower sedimentation rates and had an n- alkane composition consistent with increased marine inputsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156217/4/palo20901-sup-0002-2020PA003849-fs01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156217/3/palo20901_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156217/2/palo20901.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156217/1/palo20901-sup-0003-2020PA003849-fs02.pd

Calcification of the Planktonic Foraminiferaglobigerinabulloidesand Carbonate Ion Concentration Resultsfrom the Santa Barbara Basin

Planktonic foraminiferal calcification intensity, reflected by shell wall thickness, has been hypothesized to covary with the carbonate chemistry of seawater. Here we use both sediment trap and box core samples from the Santa Barbara Basin to evaluate the relationship between the calcification intensity of the planktonic foraminifera species Globigerina bulloides, measured by area density (µg/µm2), and the carbonate ion concentration of seawater ([CO32−]). We also evaluate the influence of both temperature and nutrient concentration ([PO43−]) on foraminiferal calcification and growth. The presence of two G. bulloides morphospecies with systematically different calcification properties and offset stable isotopic compositions was identified within sampling populations using distinguishing morphometric characteristics. The calcification temperature and by extension calcification depth of the more abundant “normal” G. bulloides morphospecies was determined using δ18O temperature estimates. Calcification depths vary seasonally with upwelling and were used to select the appropriate [CO32−], temperature, and [PO43−] depth measurements for comparison with area density. Seasonal upwelling in the study region also results in collinearity between independent variables complicating a straightforward statistical analysis. To address this issue, we use additional statistical diagnostics and a down core record to disentangle the respective roles of each parameter on G. bulloides calcification. Our results indicate that [CO32−] is the primary variable controlling calcification intensity while temperature influences shell size. We report a modern calibration for the normal G. bulloides morphospecies that can be used in down core studies of well‐preserved sediments to estimate past [CO32−]

Sediment Trap Data from the CARIACO Ocean Time Series (1995-2010)

The Cariaco Basin is a 1400-m-deep depression approximately 160 km long by 70 km wide located off the central Venezuelan coast . It is connected to the Atlantic Ocean by a sill ~100-m-deep, and two slightly deeper channels that breech it; Canal Centinela (146-m-deep) and Canal de la Tortuge (135-m-deep). High surface production rates and restricted circulation result in anoxic waters below ca. 275 m. The depth of the oxycline varies between 250 and 320 m and is independent of density. Rather, fluctuations in oxycline depth appear to be due to lateral intrusions of Caribbean Sea water that are linked to eddies along the continental shelf. A mooring with five sediment traps (Z, A-D) is located in the eastern Cariaco Basin. Traps A-D have been in place since November 1995. Trap A is located in oxic waters at 226 ± 6 m. Trap B is located at 407 ± 3 m and Trap D is located at 1205 ± 3 m. Trap C was located at a depth of 880 ± 2 m from Jan. 1996 to Nov. 2000, and was moved to 807 ± 2 m in Nov. 2000. A fifth trap, Z, was added in November 2003 at 110 m for the first 6 months, and at 150 m thereafter. All five sediment traps are coneshaped with a 0.5 m**2 opening that is covered with a baffle top to reduce turbulence. The mooring is deployed for six-month intervals and each sample collection cup is filled with a buffered 3.2% formalin solution as a preservative for the accumulating organic matter. The cups are numbered 1-13, with cup 1 collecting for the two-week interval immediately following deployment, and cup 13 collecting for the 2 weeks immediately before recovery

Pliocene-Pleistocene stable isotope record of ODP Site 107-653

Planktonic foraminiferal oxygen and carbon isotope analyses from Tyrrhenian Sea Ocean Drilling Program (ODP) Site 653 provide a continuous record of the Pliocene-Pleistocene paleoceanographic history of the Mediterranean. Long-term trends in oxygen isotopes primarily reflect changes in global climatic conditions, with a more local or regional signal superimposed on this record. For example, significant enrichments in 18O due to decreases in surface water temperature and/or increases in continental ice volume occurred at 3.1, 2.7, 2.1, 1.6, and 0.4 Ma. In contrast to most open-ocean results, the early Pliocene 6lsO record of Site 653 exhibits high-amplitude fluctuations indicative of very unstable climatic conditions in this region. Another unique aspect of this Mediterranean d18Orecord is the pronounced cooling at the Pliocene/Pleistocene boundary. The carbon isotope record for Site 653 also exhibits high-amplitude variability throughout the Pliocene-Pleistocene. This variability most probably reflects changes in the carbon isotopic composition of the source of Mediterranean surface waters

Flujo de partículas en la Fosa de Cariaco, resultados de dos décadas de observaciones 1995 – 2016

Las partı́culas en el mar tienen un origen orgánico o inorgánico, y sedimentan hacia aguas profundas y el fondo; factor que mantiene la vida en el océano sin luz y proceso que secuestra carbono de la hidrósfera y atmósfera. En la Fosa de Cariaco, sitio de alta productividad biológica y aguas profundas anóxicas, se mantuvo un sistema de trampas de sedimentos durante 20 años. Se actualizan los resultados del flujo de partı́culas entre 225 a 1210 m de profundidad, midiendo componentes básicos como el carbono orgánico (Corg), nitrógeno (N), ópalo (sı́lice biogénica), carbonato cálcico (CaCO3) y terrı́genos (fracción de origen litogénico). El flujo estuvo relacionado con las condiciones climáticas e hidrográficas. La variabilidad fue notable, tanto estacional como a largo plazo. Aunque el flujo total no presentó tendencias signiticativas, las proporciones de los componentes Corg, N y ópalo disminuyeron, y los de CaCO3 y los terrı́genos aumentaron, reflejando cambios en la composición del fitoplancton, fuente principal de la materia orgánica. Hubo en general una correlación positiva del flujo de Corg, N y ópalo con la producción primaria y la clorofila, aunque en la época de surgencia no se registró correlación debido a una mayor tasa de reciclado de la materia orgánica. El zooplancton tuvo influencia en el transporte hacia aguas profundas anóxicas. Cerca del fondo en Cariaco llega un flujo de materia en partı́culas de 9,32 ± 5,47 g m-2 mes-1, del cual 0,82 ± 0,35 g m-2 mes-1 es Corg, un 2,37% ± 1 % del C fijado en superficie.Particle flux in the Cariaco Basin, results of two decades of observations 1995 – 2016 Abstract:The particles in the sea have an organic or inorganic origin, and sediment towards deep waters and the bottom; factor that maintains life in the dark ocean and process that sequesters C from the hydrosphere and atmosphere. In the Cariaco Basin site with high biological productivity and deep anoxic waters, an array of sediment traps was maintained for 20 years. The results of the particle flux between 225 to 1210 m depth were updated, measuring the basic components, organic C, N, opal (biogenic silica), carbonates (CaCO3) and terrigenous (fraction of lithogenic origin). The flux was related to the climatic and hydrographic conditions. The variations were notable, both seasonal and long-term. Although the total flux did not show significant trends in the time series, the proportions of the organic carbon (Corg,), nitrogen (N) and opal components decreased over time, while calcium carbonate (CaCO3) and terrigenous materials increased, reflecting changes in the composition of phytoplankton as the bulk origin of organic matter. There was a general positive correlation of Corg, N, and opal flux with primary production and chlorophyll at the surface, although in the upwelling season there was no correlation due to a higher recycling rate of organic matter. Zooplankton had influence on transport to anoxic deep water. Near the bottom in Cariaco comes a flux of particulate matter of 9.32 ± 5.47 g m-2 month-1 of which 0.82 ± 0.35 g m-2 month-1 is Corg, which represents 2.37% ± 1% of the C fixed on the surface