The impact of sea water salinity on the morphology of Emiliania huxleyi in the plankton
We analysed the morphology of Emiliania huxleyi from globally distributed plankton samples and demonstrate that the size of E. huxleyi placoliths is highly correlated with in-situ sea surface water salinity. A standard step-wise multiple linear regression analysis was used to link morphological parameters of E. huxleyi to in-situ salinity and in-situ temperature. The best multiple regression model yielded an R2 = 0.87 with a standard residual error of 0.59 for in-situ salinity over a gradient from 32.6 to 38.8, whereas no significant correlation exists with temperature. Our analysis confirms the results recently published from sediment core-top samples (Bollmann and Herrle, 2007) and suggests that the morphology of E. huxleyi placoliths of recent and ancient sediments provide the potential to reconstruct sea surface salinities. However, the plankton-derived multiple regression model for in-situ salinities is different from that reported from Holocene sediments for annual mean salinities most probably due to taphonomic processes or biogeographically biased data sets (open ocean versus near shore).
PP74A-02 [Moved to PP71B]
Mid to late-Holocene diatom microfossils and geochemical proxies as evidence for paleoclimate in the Hudson River estuary, New York
New methodologies that combine the use of microfossil diatom assemblages, and elemental geochemistry (bromine (Br)) are being developed to assess late Holocene climatic variability in estuaries. The main idea is that in an estuary the saltwater wedge fluctuates in response to the volume of fluvial discharge that depends on surface runoff from precipitation and melting of snow (spring freshet). During times of high precipitation the saltwater wedge is pushed seaward. In contrast, during times of drought the saltwater wedge moves landward into the estuary. The Hudson River estuary in New York was flooded by marine waters in the early Holocene and at present its sedimentation patterns are in a state of dynamic equilibrium. Guided by high-resolution multibeam bathymetry, sediment cores (∼6 m in length) were recovered from the oligohaline parts of the estuary where discharge and precipitation changes have more impact on the saltwater wedge fluctuations. In those cores that showed continuous sedimentation, diatom assemblages and Br (ppm) were studied and used as proxies for salinity. Diatom assemblages (marine, freshwater and brackish) were identified and counted and Br (ppm) was measured by X-ray fluorescence spectrometry with an Innov-X portable system. The results were calibrated to an Pb-210 age model and compared with instrumental data of precipitation, river discharge, and Palmer Drought Severity Index (PDSI), The results obtained from two different locations show that marine diatom abundance and Br content correlate with periods of high precipitation during 1992-1988; 1985-1980; 1976-1968; 1962-1958; and increase with periods of low precipitation or droughts in 1987-1985; 1980-1975; 1967-1962; 1943-1938. The mid to late Holocene record shows a variability on the scale of ∼300 to 400 years similar to that obtained by Cronin et al. (2003) for Chesapeake Bay and related to the North Atlantic Oscillation. From 1992 to the present, both marine diatoms and Br ppm increase dramatically and do not correlate to the precipitation record. This increase in salinity is observed in all the cores and could be the result of relative sea level rise into the estuary.
Testing Foraminiferal Taphonomy as a Paleo-Tsunami Indicator in an Arid System Lagoon: Sur Lagoon, Sultanate of Oman
On 28 November 1945 a M8.1 subduction zone earthquake which occurred approximately 300 km west of
Karachi, Pakistan resulted in a 2-13 m tsunami which reportedly killed 4000 people. Limited historical
records show that the Makran Subduction Zone (MSZ) located off the coast of Pakistan has been seismically
active and has produced tsunamigenic earthquakes in the past which have impacted the coasts of Iran,
Pakistan, India and Oman. However, little is known about the longterm seismicity or tsunami generating
capacity of the MSZ, and models for future events are largely based on the limited historical information as no
geologic (i.e. tsunami deposit) evidence has been available.
Bivalve taphonomy was used in the intertidal Sur Lagoon, Oman to discriminate the 1945 tsunami deposit in trench sections. However, to find older tsunami deposits in the lagoon requires the use of vibracore studies where shell taphonomy is less applicable due the small sample sizes. Here we test the utility of foraminifera (provenance and taphonomy) for detecting and interpreting paleo-tsunami events using the 1945 tsunami shell bed as a guide. The tsunami unit in the eight cores is characterized by a dominant marine assemblage including allochthonous Amphistegina lessonii, Amphistegina lobifera, Ammonia inflata and planktics. The taphonomic characters of this assemblage include low fragmentation, high corrosion, and abundant sediment-filled fossil foraminifera with increased average specimen size. The lack of fragmentation is likely due to the high energy conditions outside the lagoon that breakdown the fragile specimens favouring the larger more robust foraminifera species (i.e. Amphistegina sp.). In contrast, the Lagoonal facies is characterized by Ammonia tepida, Elphidium gerthi and Elphidium advenum with high fragmentation, low abundance of fossil foraminifera, and decreased average specimen size. The high abundance of fragmented specimens is likely due to transport from outside of the lagoon through storms and tidal currents. These trends match species and taphonomic distributions found in the analysis of surface samples from the lagoon and shallow marine environment. However, the microfossil trends alone may not be sufficient to discriminate between a storm and tsunami deposit, although, they may prove useful when combined with shell taphonomy and particle-size analysis as a multi proxy tsunami indicator.
Environmental reconstruction of a Mexican flooded cave system: evidence for climate-forced changes to the local freshwater lens
Three radiocarbon-dated sediment cores (4.2 kya to present) from Aktun Ha (Carwash) Cave, Mexico indicate that sediments in flooded caves document Holocene environmental changes. Three distinct environmental phases were determined based on microfossils (shelled rhizopods), organic geochemistry (δ13C, δ15N, TOC, TN, C/N), and particle size distributions (PSDs). In the three cores, terrestrial organic matter was more prevalent in the core closer to the cave entrance (cenote), whereas, aquatic organic matter was more prevalent in cores deeper into the cave. Euryhaline foraminifera (78%) indicate high oligohaline conditions in the freshwater lens (salinity 3.5 - 5.0 psu) during Phase 1 (preceding 4.3 kya), which had higher hydrologic flow rates as interpreted from low organic OM deposition (less than 10%). Phase 2 (4.2 - 2.7 ky BP) is characterized by oscillations between testate amoebae (centropyxids), euryhaline foraminifera (Ammonia tepida var. juvenile), and variable δ15N values. The increases in testate amoebae from Phase 1 and up to 2.5‰ enrichment in δ15N values coupled with poorly sorted PSDs indicate repeated freshening of the freshwater lens (ca. 3.5 - 2.5 psu shift) and associated transport of terrestrial organic matter into the cave. Phase 3 is marked by the colonization of Lagenodifflugia vas at 2.76 ky BP, indicating the onset of modern salinity (1.5 psu) conditions in the local freshwater lens. This is synchronous with a significant reduction in the C/N ratio, and long-term stabilization in sedimentation. The onset of modern hydrologic flow rates in the freshwater lens (less than 1.5 m/s) contributes to increased algae populations in the cenote, increased abundance of organic matter in the cave (TOC greater than 46%). The observed environmental shifts in the cave sediments correlate well with local precipitation changes and storm activity associated with southward migration of the Intertropical Convergence Zone during the late Holocene. Importantly, these results indicate (1) that climate exudes greater control on the phreatic cave environment and aquifer than previously documented, and (2) sediment accumulations in phreatic caves contain viable climate archives, which represent a significantly unexplored source of paleoclimate data.
Sedimentation Patterns in the Rio Cruces After the May 1960 Chilean Earthquake and Tsunami
The May 22nd 1960 Chilean earthquake was the largest earthquake on record with a magnitude 9.5. The event caused extensive subsidence and uplift over wide areas (at least 130,000 km2) with uplift on the offshore South American Plate margin and downwarping in the coastal and landward areas which ranged in magnitude from 1-2 m. Widespread damage occurred along the coast from the seismic shaking and the subsequent three tsunamis with the disaster area extending at least 800 km in a N-S direction. This study of 139 cores from the subtidal areas of the Rio Cruces demonstrates the potential of using detailed particle-size distribution (PSD) plots and thecamoebians as a tool for determining older coseismic subsidence events for the Valdivia area. The PSDs and thecamoebians differentiated three main facies which included: 1) the 1960 floodplain soil horizon, 2) the tsunami unit, and 3) the post-subsidence, riverine sediment infilling. In the floodplain soil horizon, thecamoebian abundances and diversities were characteristically low, and often contained monospecific assemblages of Difflugia globulus, but also occasionally Corythion. In moister soil horizons, Centropyxis spp. were also found but in very low abundances. The thecamoebians in the tsunami unit ranged between very low to low abundances and contained slightly higher diversities including species from the flooplain soil facies and aquatic species such as Centropyxis aculeata, Centropyxis constricta and Difflugia protaeiformis. The riverine sedimentation unit was characterized by abundant thecamoebian tests and high diversities compared to the underlying facies with species compositions typical of lacustrine or slow moving river systems (Difflugia oblonga, Centropyxis constricta, Centropyxis aculeata, Lagenodifflugia vas, Difflugia protaeiformis). Based on the accumulation of sediment since the 1960 subsidence event, the Rio Cruces wetland will likely return to its pre-1960 condition in less than 100 yrs (approx. 50 yrs from present) and be poised to record another seismic event based on the reoccurrence interval of several centuries as found by Cisternas et al. (2005). Between 1960 and 2008 the water depths in the estuary were reduced by more than half, to an average water depth of less than 1 m due to 60 to 80 cm of sedimentation over that period. 210Pb and 137Cs dating of the sediments indicate the rate of sedimentation has increased significantly since 2000 and baffling by emergent wetlands will prevent erosion with the shallowing water depth. This relatively thick sediment accumulation (approx. 2 m) may allow better preservation of the underlying subsidence event with emergent floodplain soil development. This rapid readjustment of the river and wetland system along with low erosion potential, suggests that older cycles maybe found in deeper cores and might provide another paleoseismic record to assess seismic hazards for southern Chile.
A 900-Year Diatom and Chrysophyte Record of Spring Mixing and Summer Stratification From Varved Lake Mina, West-Central Minnesota, USA
A high-resolution, independent pollen-inferred paleoclimate record and direct algal seasonality data from the actual time of sediment deposition are used to interpret the high-resolution diatom and chrysophyte record of varved Lake Mina, west-central Minnesota, USA during AD 1116-2002. This direct algal seasonality information was obtained by a new technique of splitting varves into constituent winter-spring and summer lamina, and separately analyzing the siliceous algae in each layer. Analyses of integrated, continuous four-year diatom and chrysophyte samples from a sedimentary sequence show that the time period AD 1116-1478 (i.e. the Atlantic- centered Medieval Climate Anomaly (MCA)) was characterized by periods of vigorous and prolonged spring mixing, suggesting that ice-out occurred early. However, the warm summer temperatures in the MCA, particularly in a massive drought spanning AD 1300-1400, frequently caused the lake to stratify strongly, leading to nutrient depletion. During AD 1478-1870 (i.e. the Atlantic-centered Little Ice Age (LIA)), Lake Mina was characterized by weak spring circulation and increasing nutrient depletion, suggesting late ice-out conditions. Strong summer stratification and/or nutrient depletion in both time periods is shown by the occurrence of the nutrient-poor oligotrophic taxon Cyclotella pseudostelligera. The diatom and chrysophyte assemblages of the period of Euro-American settlement AD 1870-2002 show higher nutrient availability and increased spring mixing intensity, due to forest clearance and increasingly earlier ice-out (documented in regional historical records).
Monitoring seasonal variations of thecamoebians (testate amoebae) both living and total assemblages in aquatic environments in Northern Alberta
Thecamoebians (testate amoebae) have been identified in surface sediments from a series of oil sands reclamation wetlands in northeastern Alberta. The community appears to respond to a variety of different chemical parameters in aquatic ecosystems impacted by oil sands operations. To further understand the significance of the presence or absence of various strains, a seasonal study was conducted over a five-month period from May to September in a constructed aquatic environment on Syncrude property. The total thecamoebian population experiences strain-level variation on a monthly basis, influenced by climate and micro-environmental changes. Highly variable living populations are associated with the monthly strain variation, but the total abundance of the thecamoebian population as well as the relative abundance of centropyxids vs. difflugiids remained relatively constant over the course of the study. This reflects taphonomic skewing of the fossil assemblages, as preservation potential varies between species and strains. This has important implications for the use of thecamoebians as paleoenvironmental indicators. Cucurbitella tricuspis remained an important component of the thecamoebian population from May to August, August being the month when the highest proportion of its population was alive, while in September its numbers decreased significantly. Interestingly in July the dominant thecamoebian was Difflugia amphora, a rarely observed strain in the fossil record. September harbors significant increases in both the Difflugia urceolata and Pontigulasia compressa populations, consistent with research suggesting that both strains tolerate low temperatures. Difflugia oblonga remained relatively ubiquitous throughout the study, its living population increased during the late summer months of July and August, then its total numbers decreased significantly in September. Understanding the seasonality helps to distinguish thecamoebians with high fossilization potential. Remediation studies should focus on thecamoebians with high fossilization potential for reproducible results.
Monitoring the Effects of Oil Sands Process-Affected Water (OSPW) on Thecamoebian Assemblages: An Experimental Approach
Thecamoebian (testate amoeba) assemblages have been shown to respond over short time periods to environmental conditions in aquatic reclamation options under development at oil sands operations in northeastern Alberta. This makes them a useful bio-monitoring tool for assessing reclamation success. Thecamoebian responses to Oil Sands Process Water (OSPW) have been monitored in the field at lacustrine and wetland test sites established by Syncrude Canada Ltd. and Suncor Energy Ltd. These field studies have confirmed that the generation times of testate amoebas is sufficiently rapid to permit the construction of a controlled laboratory experiment to be completed within one year, where controlled exposures of a natural assemblage of thecamoebians to OSPW can be undertaken to better understand the community responses to stressors We intend to culture these protists in the lab and monitor their response to different concentrations of OSPW in a controlled environment. Survival and changes in relative community composition (difflugiids vs. centropyxids) will be used to establish the dilution of OSPW in which thecameobians can survive and examine how a natural assemblage changes over time in response to increased concentrations of OSPW. This will assist in reclamation management in the Oil Sands region of Alberta.