297 research outputs found
How have recent temperature changes affected the efficiency of ocean biological carbon export?
The ocean's large, microbially mediated reservoirs of carbon are intimately connected with atmospheric CO2 and climate, yet quantifying the feedbacks between them remains an unresolved challenge. Through an idealized mechanistic model, we consider the impact of documented climate change during the past few decades on the efficiency of biological carbon export out of the surface ocean. This model is grounded in universal metabolic phenomena, describing export efficiency's temperature dependence in terms of the differential temperature sensitivity of phototrophic and heterotrophic metabolism. Temperature changes are suggested to have caused a statistically significant decrease in export efficiency of 1.5%â±â0.4% over the past 33 yr. Larger changes are suggested in the midlatitudes and Arctic. This interpretation is robust across multiple sea surface temperature and net primary production data products. The same metabolic mechanism may have resulted in much larger changes e.g., in response to the large temperature shifts between glacial and interglacial time periods
Archaeological Survey in Guadalajara: Human Occupation in Central Spain during the Late Pleistocene
The central Meseta is a high plateau located in the heart of the Iberian Peninsula. Abundant evidence of Lower and Middle Palaeolithic occupations of the region contrasts with scarce evidence of a human presence during the early Upper Palaeolithic. On this basis, it has been suggested that climatic downturns triggered the temporary abandonment, or near abandonment, of the central Meseta during the Last Glacial period. We conducted three archaeological surveys in Guadalajara province, located in the southern part of the region, in 2009, 2010, and 2017. Survey results, interpreted in the light of a habitat suitability model, support a hypothesis of climate-driven abandonment (or near-abandonment) of the central plateau during the Last Glacial Maximum and suggest that the Tagus River Valley, which links the Spanish interior to the Atlantic seaboard, was a focus for the Palaeolithic occupation of the region at other times
Determination of the standard deviation for proficiency assessment from past participantâs performances
The âuncertainty functionâ introduced by Thompson et al. estimates the reproducibility standard deviation (SR) as a function of concentration. This model was successfully applied to a data set derived from three proficiency testing schemes aiming at the quantification of three toxic elements (cadmium, lead and mercury) in blood and urine. A threshold concentration was determined for each element. Below this concentration SR is found to be constant, while above it the reproducibility relative standard deviation is constant. This model allows the a priori estimation of standard deviation for performance assessment for proficiency testing rounds.JRC.D.5-Standards for Food Bioscienc
Determination of the standard deviation for proficiency assessment from past participant's performances
The "uncertainty function" introduced by Thompson et al. estimates the reproducibility standard deviation as a function of concentration or mass fraction. This model was successfully applied to data derived from three proficiency testing schemes aiming at the quantification of cadmium, lead and mercury in blood and urine. This model allows the estimation of standard deviation for the performance assessment for proficiency testing rounds
Satellite Lidar Measurements as a Critical New Global Ocean Climate Record
The year 2023 marked the tenth anniversary of the first published description of global ocean plankton stocks based on measurements from a satellite lidar. Diverse studies have since been conducted to further refine and validate the lidar retrievals and use them to discover new characteristics of plankton seasonal dynamics and marine animal migrations, as well as evaluate geophysical products from traditional passive ocean color sensors. Surprisingly, all of these developments have
been achieved with lidar instruments not designed for ocean applications. Over this same decade, we have witnessed unprecedented changes in ocean ecosystems at unexpected rates and driven by a multitude of environmental stressors, with a dominant factor being climate warming. Understanding, predicting, and responding to these ecosystem changes requires a global ocean observing network linking satellite, in situ, and modeling approaches. Inspired by recent successes, we promote here
the creation of a lidar global ocean climate record as a key element in this envisioned advanced observing system. Contributing to this record, we announce the development of a new satellite lidar mission with ocean-observing capabilities and then discuss additional technological advances
that can be envisioned for subsequent missions. Finally, we discuss how a potential near-term gap in global ocean lidar data might, at least partially, be filled using on-orbit or soon-to-be-launched lidars designed for other disciplinary purposes, and we identify upcoming needs for in situ support systems and science community development
The Palaeolithic occupation of southern Alentejo: the Sado
ABSTRACT
The Sado River Drainage Survey project (2004-2008)
was designed to fill a significant gap in our knowledge of
the prehistory of Portugal. Southern Alentejo constitutes
nearly one third of the total land mass of continental Portugal,
but has received comparatively little attention from
Palaeolithic archaeologists. Practically nothing was
known about the prehistory of the Sado River basin,
which includes the southern Alentejo plain, before now.
The results of the Sado River Drainage Survey (SRDS)
indicate that the Sado River basin was likely occupied at
low population densities during the Middle Palaeolithic.
There is some evidence for a Lower Palaeolithic presence
but little or no evidence of an Upper Palaeolithic occupation.
The emerging pattern suggests either an occupational
hiatus or a major shift in settlement pattern towards
the end of the Middle Palaeolithic. Possible explanations
for this pattern, including aridification driven by climate
change, are explored here
Tabletop imaging of structural evolutions in chemical reactions
The introduction of femto-chemistry has made it a primary goal to follow the
nuclear and electronic evolution of a molecule in time and space as it
undergoes a chemical reaction. Using Coulomb Explosion Imaging we have shot the
first high-resolution molecular movie of a to and fro isomerization process in
the acetylene cation. So far, this kind of phenomenon could only be observed
using VUV light from a Free Electron Laser [Phys. Rev. Lett. 105, 263002
(2010)]. Here we show that 266 nm ultrashort laser pulses are capable of
initiating rich dynamics through multiphoton ionization. With our generally
applicable tabletop approach that can be used for other small organic
molecules, we have investigated two basic chemical reactions simultaneously:
proton migration and C=C bond-breaking, triggered by multiphoton ionization.
The experimental results are in excellent agreement with the timescales and
relaxation pathways predicted by new and definitively quantitative ab initio
trajectory simulations
Pharmacy Refill Adherence Compared with CD4 Count Changes for Monitoring HIV-Infected Adults on Antiretroviral Therapy
Analyzing pharmacy and laboratory records from 1,982 patients beginning HIV therapy in southern Africa, Gregory Bisson and colleagues find medication adherence superior to CD4 count changes in identifying treatment failure
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