Peoenvironmental proxy development: How can we rapidly analyze marsh sediments for regional environmental change?

This study developed and implemented a new and rapid X-Ray Fluorescence (XRF) elemental analysis (Innov-X Alpha series 4000 ) method to investigate past climatic and environmental changes from the Hudson Estuary sediment record in four Hudson River National Estuarine Research Reserve (HRNERR) sites and an additional 29 sites along a north-south transect of the estuary from Troy to New York harbor. In comparison with external analysis, we developed analysis procedure and new calibration curves and to find methods suitable for the analysis of organic-rich marsh sediment which are very heterogeneous, very diluted in inorganic content, and much more difficult to analyze traditionally with XRF in comparison to lake or inorganic sediments. In combination with our existing paleoecological and radiometric chronology records, we found that 1) Ti and K are parallel to inorganic matter increases and can be used to identify landscape change, increase in erosion, and sedimentation pattern shifts. 2) Zn and Sr concentration at Piermont marsh matched charcoal and fern spore counts and peaked during the Medieval Warm Period (MWP) from 850-1350 AD. Thus, Zn and Sr may be a good proxy of drought and fire. 3) Additional elemental ratios maybe useful for the identification of sediment source and hydrological shifts. 4) Pb concentration profiles can be obtained from both wet and dry marsh and river sediment to establish a chronology (Kenna et al., 2011). The method agrees well with Ambrosia pollen count and Cs-137 and Pb-210 chronologies.

Fig. 1: Example usage of XRF analysis for rapid quantification of landscape and sediment dynamic changes in Piermont (LOI data from Pederson et al., 2005). Ti and K in marsh cores parallel inorganic matter content, which increases during land-clearing (human after the European Settlement) and erosional events (droughts of the Medieval Warm Period). (Sritrairat et al., in prep)

Selected abstract:

Method Evaluation: Coupling of Geochemical Proxies with Traditional Paleoecological Indicators in Marsh Sediments

S. Sritrairat^{1, 3}; T. C. Kenna¹; D. M. Peteet^{1, 2}
1. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, United States.
2. NASA Goddard Institute for Space Studies, New York, NY, United States.
3. Department of Earth and Environmental Sciences, Columbia University, New York, NY, United States.

Paleoclimatic and paleoecological research in estuaries is very important for understanding both marine and terrestrial responses to climate change. Marsh environments, characterized by high accumulation rates of up to 1 cm/yr and minimal mixing, offer the potential to obtain good quality paleo-records. The Hudson River Estuary in New York is an ideal study location as the estuary functions for millions of people and climate change directly affects New York City. The traditional method of paleoclimatic analysis in marshes includes the analysis of pollen, spores, and macrofossils (i.e. fossil seeds, leaves, and foraminifera) as well as the measurement of sediment physical properties. However, palynological analysis is very time consuming, making it difficult to analyze sediment cores at high resolution and with robust spatial coverage to gain a regional perspective. We are developing a new rapid analysis that provides a more efficient paleoclimate technique for marsh sediments, using X-ray fluorescence with a field portable analyzer. However, the use of geochemical proxies can be complicated by the complexity of the governing ecology, highly variable matrix, and the organic-rich nature of the sediments. We will discuss the potential and limitation of the method, including the calibration of the method to analyze wet and dry marsh sediments. We will present a comparison of elemental distribution and elemental ratio profiles with pollen, macrofossil, and sediment profiles during late Holocene from several Hudson Estuary marshes (i.e. Piermont Marsh, Iona Island Marsh, and Tivoli North Bay Marsh). Work to date suggests that geochemical proxies can be used to identify droughts, hydrological shifts, fires, and landscape alteration. Examples of key elements include Ti, K, and Zn. We will also present base-line modern analog study of the elemental composition of sediments originating from major tributaries of the Hudson Estuary and their application of sediment source indicators and hydrological changes in geological records.

Sritrairat, S. Kenna, T.C., Peteet, D.M. 2009. Method Evaluation: Coupling of Geochemical Proxies with Traditional Paleoecological Indicators in Marsh Sediments. Eos Trans. AGU, 90(54), Fall Meet. Suppl., Abstract PP31B-1351