49 research outputs found
Seismic interpretation of pelagic sedimentation regimes in the 18–53 Ma eastern equatorial Pacific : basin-scale sedimentation and infilling of abyssal valleys
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q03004, doi:10.1029/2010GC003347.Understanding how pelagic sediment has been eroded, transported, and deposited is critical to evaluating pelagic sediment records for paleoceanography. We use digital seismic reflection data from an Integrated Ocean Drilling Program site survey (AMAT03) to investigate pelagic sedimentation across the eastern-central equatorial Pacific, which represents the first comprehensive record published covering the 18–53 Ma eastern equatorial Pacific. Our goals are to quantify (1) basin-hill-scale primary deposition regimes and (2) the extent to which seafloor topography has been subdued by abyssal valley-filling sediments. The eastern Pacific seafloor consists of a series of abyssal hills and basins, with minor late stage faulting in the basement. Ocean crust rarely outcrops at the seafloor away from the rise crest; both hills and basins are sediment covered. The carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data. Overall, we recognized three different sedimentation regimes: depositional (high sedimentation rate), transitional, and minimal sedimentation (low sedimentation rate) regimes. In all areas, the sedimented seafloor mimics the underlying basement topography, although the degree to which topography becomes subdued varies. Depositional regimes result in symmetric sedimentation within basins and subdued topography, whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief. Regardless of sedimentation regime, enhanced sediment deposition occurs within basins. However, we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills. If this variation is due to sediment focusing, the focusing factor in the basins, as measured by 230Th, is no more than a factor of ∼1.3 of the total vertical particulate rain.This research is supported by NSF grants OCE‐07253011
and OCE‐0851056 (M. Lyle and M. Tominaga) and NERC
grant NE/C508985/2 (N. C. Mitchell)
The Contribution of Occult Precipitation to Nutrient Deposition on the West Coast of South Africa
The Strandveld mediterranean-ecosystem of the west coast of South Africa supports floristically
diverse vegetation growing on mostly nutrient-poor aeolian sands and extending from
the Atlantic Ocean tens of kilometers inland. The cold Benguela current upwelling interacts
with warm onshore southerly winds in summer causing coastal fogs in this region. We hypothesized
that fog and other forms of occult precipitation contribute moisture and nutrients
to the vegetation. We measured occult precipitation over one year along a transect running
inland in the direction of the prevailing wind and compared the nutrient concentrations with
those in rainwater. Occult deposition rates of P, N, K, Mg, Ca, Na, Al and Fe all decreased
with distance from the ocean. Furthermore, ratios of cations to Na were similar to those of
seawater, suggesting a marine origin for these. In contrast, N and P ratios in occult precipitation
were higher than in seawater. We speculate that this is due to marine foam contributing
to occult precipitation. Nutrient loss in leaf litter from dominant shrub species was
measured to indicate nutrient demand. We estimated that occult precipitation could meet
the demand of the dominant shrubby species for annual N, P, K and Ca. Of these species,
those with small leaves intercepted more moisture and nutrients than those with larger
leaves and could take up foliar deposits of glycine, NO3-, NH4
+ and Li (as tracer for K)
through leaf surfaces. We conclude that occult deposition together with rainfall deposition
are potentially important nutrient and moisture sources for the Strandveld vegetation that
contribute to this vegetation being floristically distinct from neighbouring nutrient-poor Fynbos
vegetation
In vitro co-cultures of Pinus pinaster with Bursaphelenchus xylophilus: a biotechnological approach to study pine wilt disease
Abstract
Main conclusion Co-cultures of Pinus pinaster with
Bursaphelenchus xylophilus were established as a
biotechnological tool to evaluate the effect of nematotoxics
addition in a host/parasite culture system.
The pinewood nematode (PWN), Bursaphelenchus xylophilus,
the causal agent of pine wilt disease (PWD), was
detected for the first time in Europe in 1999 spreading
throughout the pine forests in Portugal and recently in
Spain. Plant in vitro cultures may be a useful experimental
system to investigate the plant/nematode relationships in
loco, thus avoiding the difficulties of field assays. In this
study, Pinus pinaster in vitro cultures were established and
compared to in vivo 1 year-old plantlets by analyzing shoot
structure and volatiles production. In vitro co-cultures were
established with the PWN and the effect of the phytoparasite
on in vitro shoot structure, water content and
volatiles production was evaluated. In vitro shoots showed
similar structure and volatiles production to in vivo maritime
pine plantlets. The first macroscopic symptoms of
PWD were observed about 4 weeks after in vitro co-culture
establishment. Nematode population in the culture medium
increased and PWNs were detected in gaps of the callus
tissue and in cavities developed from the degradation of
cambial cells. In terms of volatiles main components,
plantlets, P. pinaster cultures, and P. pinaster with B. xylophilus
co-cultures were all b- and a-pinene rich. Cocultures
may be an easy-to-handle biotechnological approach
to study this pathology, envisioning the understanding
of and finding ways to restrain this highly
devastating nematode.
Keywords Maritime pine ! Monoxenic culture !
Pinewood nematode ! Relative water content ! Shoots
structure ! Volatiles
Abbreviations
BAP 6-Benzylaminopurine
DAI Days after inoculation
EPPO European and Mediterranean Plant Protectio
In vitro co-culture of Solanum tuberosum hairy roots with Meloidogyne chitwoodi: structure, growth and production of volatiles
In vitro co-cultures of Pinus pinaster with Bursaphelenchus xylophilus: a biotechnological approach to study pine wilt disease
Team Dynamics Theory: Nomological network among cohesion, team mental models, coordination, and collective efficacy
I put forth a theoretical framework, namely Team Dynamics Theory (TDT), to address the need for a parsimonious yet integrated, explanatory and systemic view of team dynamics. In TDT, I integrate team processes and outputs and explain their relationships within a systemic view of team dynamics. Specifically, I propose a generative nomological network linking cohesion, team mental models, coordination, collective efficacy, and team outcomes. From this nomological conceptualization, I illustrate how myriad alternative models can be derived to account for variance in different working teams, each comprised of unique members, and embedded in singular contexts. I outline TDT’s applied implications for team development, the enhancement of team functioning, and the profiling of team resilience. I conclude by discussing how TDT’s ontological and nomological propositions can be tested through various theoretical inquiries, methodological approaches, and intervention-based studies