Jeomshik Hwang

The composition and formation mechanisms of the uncharacterized fraction of oceanic particulate organic carbon (POC) are not well understood. We isolated biologically important compound classes and the acid-insoluble fraction, a proxy of the uncharacterized fraction, from sinking POC in the deep Northeast Pacific and measured carbon isotope ratios to constrain the source(s) of the uncharacterized fraction. Stable carbon and radiocarbon isotope signatures of the acid-insoluble fraction were simil

Particulate organic carbon (POC) in the ocean often exhibits more depleted radiocarbon contents (lower Δ 14 C values) than expected if its sole source were POC recently synthesized by primary production and export from the overlying surface waters. An examination of available Δ 14 C data sets for sinking POC show that this phenomenon is both common and globally widespread. Also, a strong correlation is found to exist between Δ 14 C values of organic carbon and aluminum content in sinking particl

We report electrical transport through 60 base pairs of poly(dG)-poly(dC) DNA molecules. The DNA solution is dropped on two metal electrodes with the gap of 20 nm. The current–voltage characteristics measured between the electrodes exhibits clear staircases, which are reproducible over repeated measurements. The size of the observed staircases is consistent with the energy gap obtained from a tight binding calculation.

Understanding the processes driving the carbon cycle in the Arctic Ocean is important for assessing the impacts of the predicted rapid and amplified climate change in this region. We analyzed settling particle samples intercepted by a time‐series sediment trap deployed in the abyssal Canada Basin (at 3067 m) in order to examine carbon export to the deep Arctic Ocean. Strikingly old radiocarbon ages (apparent mean 14 C age = ∼1900 years) of the organic carbon, abundant lithogenic material (∼80%),

Surface sediments along a transect from an abyssal site in the northeastern Pacific (Station M, 34°50′N, 123°00′W) to a small mountainous river on the California coast (Santa Clara River) were studied to investigate the sources and cycling of organic matter on the continental margin. Sediment samples were separated into organic compound fractions (extractable lipids, amino acids (THAA), carbohydrates (TCHO), and the acid‐insoluble fraction), and their carbon isotope ratios were measured. The Δ 1

Abstract The Amundsen Sea polynya (ASP) is reportedly the most productive among the coastal polynyas around Antarctica. However, observational constraints limit our understanding of the biological pump and carbon cycle in the ASP. We measured various carbon‐related parameters such as primary production, bacterial production, sinking flux of particulate organic carbon (POC), and accumulation of organic carbon in the sediment as well as hydrographic parameters during field observations and by inst

Abstract To better understand the current carbon cycle and potentially detect its change in the rapidly changing Arctic Ocean, we examined sinking particles collected quasi‐continuously over a period of 7 years (2004–2011) by bottom‐tethered sediment trap moorings in the central Canada Basin. Total mass flux was very low (<100 mg m −2 d −1 ) at all sites and was temporally decoupled from the cycle of primary production in surface waters. Extremely low radiocarbon contents of particulate organ

Contaminant carbon (blank carbon) was studied for its impact on the carbon isotope measurements (Δ 14 C and δ 13 C) of 3 organic compound classes of oceanic particulate organic matter. Two methods of blank correction and associated uncertainties were studied. First, the carbon blanks were quantified manometrically and the isotope ratios of the blank carbon were measured directly. Second, the isotope ratios of the blank carbon were estimated using the standard dilution method from the difference

A 6‐year time series of Δ 14 C, δ 13 C, and C/N measurements in deep sinking particulate organic matter (POM) is presented for an abyssal site, Station M in the northeast Pacific Ocean. The Δ 14 C values revealed that sinking POM at 3450 m depth (650 m above bottom) contained old carbon despite its presumed short transit time in the water column. The isotopic and chemical properties of the sinking POM varied with time and appear to be controlled by more than one major process. In 1993, 1994, and

We demonstrate the effect of Ti thickness on the contact resistance between GaN nanowires and Ti∕Au electrodes. We have carried out systematic characterization of many GaN nanowires contacted by various Ti∕Au electrodes. We conclude that the average resistance is reduced by almost six orders of magnitude as Ti thickness increases from 0 to 20nm, and the resistance value then saturates when the Ti thickness further increases. Our observation can be explained by the formation of TiOx through the r

Abstract The export of particulate organic carbon (POC) from surface waters to the ocean interior via the biological carbon pump is largely envisioned as a vertical process. However, several lines of evidence suggest that lateral supply of aged organic matter hosted on lithogenic particles derived from sediment resuspension may also be a significant process. Despite its potential importance, lateral POC supply has not been systematically examined on a global scale. Here, we assess the contributi