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R. Murray

Publications and source records attributed to R. Murray.

4 recordsLinked to original sources
USGS2015

Quantifying soil carbon loss and uncertainty from a peatland wildfire using multi-temporal LiDAR

Peatlands are a major reservoir of global soil carbon, yet account for just 3% of global land cover. Human impacts like draining can hinder the ability of peatlands to sequester carbon and expose their soils to fire under dry conditions. Estimating soil carbon loss from peat fires can be challenging due to uncertainty about pre-fire surface elevations. This study uses multi-temporal LiDAR to obtain pre- and post-fire elevations and estimate soil carbon loss caused by the 2011 Lateral West fire in the Great Dismal Swamp National Wildlife Refuge, VA, USA. We also determine how LiDAR elevation error affects uncertainty in our carbon loss estimate by randomly perturbing the LiDAR point elevations and recalculating elevation change and carbon loss, iterating this process 1000 times. We calculated a total loss using LiDAR of 1.10 Tg C across the 25 km 2 burned area. The fire burned an average of 47 cm deep, equivalent to 44 kg C/m 2 , a value larger than the 1997 Indonesian peat fires (29 kg C/m 2 ). Carbon loss via the First-Order Fire Effects Model (FOFEM) was estimated to be 0.06 Tg C. Propagating the LiDAR elevation error to the carbon loss estimates, we calculated a standard deviation of 0.00009 Tg C, equivalent to 0.008% of total carbon loss. We conclude that LiDAR elevation error is not a significant contributor to uncertainty in soil carbon loss under severe fire conditions with substantial peat consumption. However, uncertainties may be more substantial when soil elevation loss is of a similar or smaller magnitude than the reported LiDAR error.

Virginia↗
USGS2010

Using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to explore geochemical taphonomy of vertebrate fossils in the upper cretaceous two medicine and Judith River formations of Montana

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine rare earth element (REE) content of 76 fossil bones collected from the Upper Cretaceous (Campanian) Two Medicine (TMF) and Judith River (JRF) Formations of Montana. REE content is distinctive at the formation scale, with TMF samples exhibiting generally higher overall REE content and greater variability in REE enrichment than JRF samples. Moreover, JRF bones exhibit relative enrichment in heavy REE, whereas TMF bones span heavy and light enrichment fields in roughly equal proportions. TMF bones are also characterized by more negative Ce anomalies and greater U enrichment than JRF bones, which is consistent with more oxidizing diagenetic conditions in the TMF. Bonebeds in both formations show general consistency in REE content, with no indication of spatial or temporal mixing within sites. Previous studies, however, suggest that the bonebeds in question are attritional assemblages that accumulated over considerable time spans. The absence of geochemical evidence for mixing is consistent with diagenesis transpiring in settings that remained chemically and hydrologically stable during recrystallization. Lithology-related patterns in REE content were also compared, and TMF bones recovered from fluvial sandstones show relative enrichment in heavy REE when compared with bones recovered from fine-grained floodplain deposits. In contrast, JRF bones, regardless of lithologic context (sandstone versus mudstone), exhibit similar patterns of REE uptake. This result is consistent with previous reconstructions that suggest that channel-hosted microfossil bonebeds of the JRF developed via the reworking of preexisting concentrations embedded in the interfluve. Geochemical data further indicate that reworked elements were potentially delivered to channels in a recrystallized condition, which is consistent with rapid adsorption of REE postmortem. Copyright ?? 2010, SEPM (Society for Sedimentary Geology).

Palaios↗
USGS1991

Rare earth elements in Japan Sea sediments and diagenetic behavior of Ce/Ce∗: results from ODP Leg 127

The relative effects of paleoceanographic and paleogeographic variations, sediment lithology, and diagenetic processes on the recorded rare earth element (REE) chemistry of Japan Sea sediments are evaluated by investigating REE total abundances and relative fractionations in 59 samples from Ocean Drilling Program Leg 127. REE total abundances (ΣREE) in the Japan Sea are strongly dependent upon the paleoceanographic position of a given site with respect to terrigenous and biogenic sources. REE concentrations at Site 794 (Yamato Basin) overall correspond well to aluminosilicate chemical indices and are strongly diluted by SiO 2 within the late Miocene-Pliocene diatomaceous sequence. Eu/Eu* values at Site 794 reach a maximum through the diatomaceous interval as well, most likely suggesting an association of Eu/Eu* with the siliceous component, or reflecting slight incorporation of a detrital feldspar phase. ΣREE at Site 795 (Japan Basin) also is affiliated strongly with aluminosilicate phases, yet is diluted only slightly by siliceous input. At Site 797 (Yamato Basin), REE is not as clearly associated with the aluminosilicate fraction, is correlated moderately to siliceous input, and may be sporadically influenced by detrital heavy minerals originating from the nearby rifted continental fragment composing the Yamato Rise. The biogenic influence is largest at Site 794, moderately developed at Site 797, and of only minor importance at Site 795, reflecting basinal contrasts in productivity such that the Yamato Basin records greater biogenic input than the Japan Basin, while the most productive waters overlie the easternmost sequence of Site 794. Ce/Ce* profiles at all three sites increase monotonically with depth, and record progressive diagenetic LREE fractionation. The observed Ce/Ce* record does not respond to changes in oxygenation state of the overlying water, and Ce/Ce* correlated slightly better with depth than with age. The downhole increase in Ce/Ce* at Site 794 and Site 797 is a passive response to diagenetic transfer of LREE (except Ce) from sediment to interstitial water. At Site 795, the overall lack of correlation between Ce/Ce* and L (l n /Yb n suggests that other processes are occurring which mask the diagenetic behavior of all LREEs. First-order calculations of the Ce budget in Japan Sea waters and sediment indicate that ~20% of the excess Ce adsorbed by settling particles is recycled within the water column, and that an additional ~38% is recycled at or near the seafloor (data from Masuzawa and Koyama, 1989). Thus, because the remaining excess Ce is only ~10% of the total Ce, there is not a large source of Ce to the deeply buried sediment, further suggesting that the downhole increase in Ce/Ce* is a passive response to diagenetic behavior of the other LREEs. The REE chemistry of Japan Sea sediment therefore predicts successive downhole addition of LREEs to deeply-buried interstitial waters.

Geochimica et Cosmochimica Acta↗