The Influence of Particle Concentration and Bulk Characteristics on Polarized Oceanographic Lidar Measurements

Oceanographic lidar measurements of the linear depolarization ratio, δ, contain information on the bulk characteristics of marine particles that could improve our ability to study ocean biogeochemistry. However, a scarcity of information on the polarized light-scattering properties of marine particles and the lack of a framework for separating single and multiple scattering effects on δ have hindered the development of polarization-based retrievals of bulk particle properties. To address these knowledge gaps, we made single scattering measurements of δ for several compositionally and morphologically distinct marine particle assemblages. We then used a bio-optical model to explore the influence of multiple scattering and particle characteristics on lidar measurements of δ made during an expedition to sample a mesoscale coccolithophore bloom. Laboratory measurements of linear depolarization revealed a complex dependency on particle shape, size, and composition that were consistent with scattering simulations for idealized nonspherical particles. Model results suggested that the variability in δ measured during the field expedition was driven predominantly by shifts in particle concentration rather than their bulk characteristics. However, model estimates of δ improved when calcite particles were represented by a distinct particle class, highlighting the influence of bulk particle properties on δ. To advance polarized lidar retrievals of bulk particle properties and to constrain the uncertainty in satellite lidar retrievals of particulate backscattering, these results point to the need for future efforts to characterize the variability of particulate depolarization in the ocean and to quantify the sensitivity of operational ocean lidar systems to multiple scattering

Dimethylamine in cloud water: a case study over the northwest Atlantic Ocean

This study analyzes characteristics of an important alkyl amine species, dimethylamine (DMA), in cloud water over the northwest Atlantic. Data were gathered from the winter and summer 2020 deployments of the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) on board the HU 25 Falcon

Direct application of compound-specific radiocarbon analysis of leaf waxes to establish lacustrine sediment chronology

Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Paleolimnology 39 (2008): 43-60, doi:10.1007/s10933-007-9094-1.This study demonstrates use of compound-specific radiocarbon analysis (CSRA) for dating Holocene lacustrine sediments from carbonate-hosted Ordy Pond, Oahu, Hawaii. Long-chain odd-numbered normal alkanes (n-alkanes), biomarkers characteristic of terrestrial higher plants, were ubiquitous in Ordy Pond sediments. The δ13C of individual n-alkanes ranged from −29.9 to −25.5‰, within the expected range for n-alkanes synthesized by land plants using the C3 or C4 carbon fixation pathway. The 14C ages of n-alkanes determined by CSRA showed remarkably good agreement with 14C dates of rare plant macrofossils obtained from nearby sedimentary horizons. In general, CSRA of n-alkanes successfully refined the age-control of the sediments. The sum of n-alkanes in each sample produced 70–170 μg of carbon (C), however, greater age errors were confirmed for samples containing less than 80 μg of C. The 14C age of n-alkanes from one particular sedimentary horizon was 4,155 years older than the value expected from the refined age-control, resulting in an apparent and arguable age discrepancy. Several lines of evidence suggest that this particular sample was contaminated by introduction of 14C-free C during preparative capillary gas chromatography. This study simultaneously highlighted the promising potential of CSRA for paleo-applications and the risks of contamination associated with micro-scale 14C measurement of individual organic compounds.This project was funded by Petroleum Research Fund (PRF #40088-ACS) and in part by Sigma Xi, The Scientific Research Society (Grants in aid of research, 2003)

Spatially-coordinated airborne data and complementary products for aerosol, gas, cloud, and meteorological studies: The NASA ACTIVATE dataset

The NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) produced a unique dataset for research into aerosol-cloud-meteorology interactions. An HU-25 Falcon and King Air conducted systematic and spatially coordinated flights over the northwest Atlantic Ocean. This paper describes the ACTIVATE flight strategy, instrument and complementary dataset products, data access and usage details, and data application notes