Paleoclimate proxy perspective on Caribbean climate since the year 1751: Evidence of cooler temperatures and multidecadal variability

Kilbourne, K. H., T. M. Quinn, R. Webb, T. Guilderson, J. Nyberg, and A. Winter (2008), Paleoclimate proxy perspective
on Caribbean climate since the year 1751: Evidence of cooler temperatures and multidecadal variability, Paleoceanography, 23,
PA3220, doi:10.1029/2008PA001598.

Annually resolved coral delta O-18 and Sr/Ca records from southwestern Puerto Rico are used to investigate Caribbean climate variability between 1751 and 2004 C. E. Mean surface ocean temperatures in this region have increased steadily by about 2 degrees C since the year 1751, with Sr/Ca data indicating 2.1 +/- 0.8 degrees C and delta O-18 data indicating 2.7 +/- 0.5 degrees C. Coral geochemical records from across the tropics demonstrate that regional variability is important for understanding climate variations at centennial time scales. A strong multidecadal salinity signal in the oxygen isotope data correlates with observed multidecadal temperature variations in the Northern Hemisphere. Instrumental wind and precipitation data indicate that the most recent coral isotopic variations are caused by expansion and contraction of the steep regional salinity gradient, forced by trade wind anomalies through meridional Ekman transport. The timing of the fluctuations suggests that the multidecadal-scale wind and surface circulation anomalies might play a role in Atlantic temperature variability and meridional overturning circulation, but further work is needed to confirm this suggestion.

Climate and Atmosphere-- Puerto Rico

From EarthTrends: The Environmental Information Portal the Web site is a companion to the EarthTrends site, launched in 2001 by the World Resources Institute. Inside these pages you will find time-series information for over 500 variables, more than 2000 country profiles, as well as data tables, maps, and feature stories on a variety of environmental, social, and economic topics. Click here to learn more about EarthTrends.

Clouds and aerosols in Puerto Rico – a new evaluation

Allan, J.D., et al., 2007. Clouds and aerosols in Puerto Rico — a new evaluation. Atmos.
Chem. Phys. Discuss. 7, 12573–12616.

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical 5 marine environment, a period of intensive measurements using some of the latest developments in online instrumentation took place in December 2004 in Puerto Rico. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040m 10 a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind 15 sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submircron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This 20 change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm−3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 gm−3 when the winds shifted from the ENE to ESE. Larger numbers 25 of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions.

Effects of land use change on northeastern Puerto Rican rivers

Clark, J. 1997. Effects of land use change on northeastern
Puerto Rican rivers. Phd Dissertation, Johns
Hopkins University, Baltimore, Maryland, 187

The 500 year period considered in this study is sufficiently long that river change may be produced by natural changes in the external controls of river geometry. These controls include changes in the base level and changes in the climate which, like land use, change the supply of sediment to the rivers.

Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes

C. Riebe, J.W. Kirchner, R. Finkel, Erosional and climatic
effects on long-term chemical weathering rates in granitic C. Riebe, J.W. Kirchner, R. Finkel, Erosional and climatic
effects on long-term chemical weathering rates in granitic

We used cosmogenic nuclide and geochemical mass balance methods to measure long-term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes. Our 42 study sites encompass widely varying climatic and erosional regimes, with mean annual temperatures ranging from 2 to 25 jC, average precipitation ranging from 22 to 420 cmyear 1, and denudation rates ranging from 23 to 755 tkm 2year 1. Long-term chemical weathering rates range from 0 to 173 tkm 2 year 1, in several cases exceeding the highest granitic weathering rates on record from previous work. Chemical weathering rates are highest at the sites with rapid denudation rates, consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock. A simple empirical relationship based on temperature, precipitation and long-term denudation rates explains 89–95% of the variation in long-term weathering rates across our network of sites. Our analysis shows that, for a given precipitation and temperature, chemical weathering rates increase proportionally with freshmaterial supply rates. We refer to this as ‘‘supply-limited’’ weathering, in which fresh material is chemically depleted to roughly the same degree, regardless of its rate of supply from breakdown of rock. The temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter-comparisons of catchment mass-balance data from the field. Our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought, at least in actively eroding, unglaciated terrain similar to our study sites. To the extent that chemical weathering rates are supply-limited in mountainous landscapes, factors that regulate rates of mineral supply from erosion, such as tectonic uplift, may lead to significant fluctuations in global climate over the long term.

Modeling the spatial and temporal variability in climate and primary productivity across the Luquillo Mountains, Puerto Rico

Wanga, Hongqing; Halla, Charles A.S.; Scatenab, Frederick N.; Fetcherc, Ned; Wua, Wei 2003. Modeling the spatial and temporal variability in climate and primary productivity across the Luquillo Mountains, Puerto Rico.. Forest Ecology and Management 179 :69-94l.

There are few studies that have examined the spatial variability of forest productivity over an entire tropical forested landscape. In this study, we used a spatially-explicit forest productivity model, TOPOPROD, which is based on the FORESTBGC model, to simulate spatial patterns of gross primary productivity (GPP), net primary productivity (NPP), and respiration over the entire Luquillo Experimental Forest (LEF) in the mountains of northeastern Puerto Rico.We modeled climate variables (e.g. solar insolation, temperature, rainfall and transpiration) using a topography-based climate model, TOPOCLIM. The simulated GPP ranged from 8 to 92 t C/ha per year with a mean of 51 t C/ha per year. The simulated NPP ranged from 0.5 to 24 t C/ha per year with a mean of 9.4 t C/ha per year. The simulated plant respiration ranged from 31 to 68 with a mean of 42 t C/ha per year. Simulated GPP and respiration declined with increased elevation whereas simulated NPP increased from low to middle elevation but decreased from middle to high elevations. Statistical analyses indicate that variation in solar insolation, which decreases with increase in elevation, is the most important factor controlling the spatial variation of forest productivity in the LEF. Validation with the limited spatial empirical data indicated that our simulations overestimated GPP by 2% for a middle elevation test site, and by 43% for a mountain peak site. Our simulations also overestimated NPP in the middle elevation Colorado forest and higher elevation Dwarf forest by 32 and 36%, respectively, but underestimated NPP in the Tabonuco and Palm forests at low to middle elevations by 9–15% and 18%, respectively. Simulated GPP and NPP would decrease under CO2 doubling as projected temperatures increase and precipitation decreases. Different forest types respond differently to potential climate change and CO2 doubling. Comparison with other tropical forests suggests that the LEF as a whole has higher GPP (51 tC/ha per year versus 40 t C/ha per year) but lower NPP (9.4 t C/ha per year versus 11 t C/ha per year) than other tropical rain forests.

Atlantic Subtropical Storms. Part II: Climatology

Guishard, Mark P., Jenni L. Evans, Robert E. Hart, 2009: Atlantic Subtropical Storms. Part II: Climatology. J. Climate, 22, 3574–3594.
doi: 10.1175/2008JCLI2346.1

A 45-yr climatology of subtropical cyclones (ST) for the North Atlantic is presented and analyzed. The STs pose a warm-season forecasting problem for subtropical locations such as Bermuda and the southern United States because of the potentially rapid onset of gale-force winds close to land. Criteria for identification of ST have been developed based on an accompanying case-study analysis. These criteria are applied here to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) to construct a consistent historical database of 197 North Atlantic ST in 45 yr. Because ST may eventually evolve into tropical cyclones, sea surface temperatures (SST) and vertical wind shear conditions for tropical cyclogenesis are contrasted with the conditions for ST genesis identified here. Around 60% of the 197 ST formed over SST in excess of 258C in a region of weak static stability. Further, the mean environmental vertical wind shear at formation for these storms is 10.7 m s21, a magnitude generally considered to be unfavorable for tropical cyclogenesis. The STs have hybrid structure, so the potential for baroclinic and thermodynamic development is explored through the baroclinic zone (characterized by the Eady growth rate s) and SST field. Seasonal evolution in the location and frequency of ST formation in the basin is demonstrated to correspond well to the changing region of overlap between SST . 258C and s . 0.1 day21. This climatology is contrasted with two alternative ST datasets. The STs contribute to 12% of tropical cyclones (TC) in the current National Hurricane Center (NHC) Hurricane Database (HURDAT); this equivalent to about 1 in 8 genesis events from an incipient ST disturbance. However, with the addition of 144 ST that are newly identified in this climatology (and not presently in HURDAT) and the reclassification (as not ST) of 65 existing storms in HURDAT, 197/597 storms (33%) in the newly combined database are ST, which emphasizes the potential importance of these warm-season storms.

Soil Oxygen Availability and Biogeochemistry along Rainfall and Topographic Gradients in Upland Wet Tropical Forest Soils

Silver W, Lugo AE, Keller M (1999) Soil oxygen availability and
biogeochemistry along rainfall and topographical gradients in
upland wet tropical forest soils. Biogeochemistry 44:301–

We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500– 5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, 150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (<3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were <3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes.We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.
Syndicate content