Tourism impacts on benthic communities of sandy beaches

This study evaluated the effect of human trampling on the benthic macrofauna of two beaches in Southeast Brazil with different levels of intensity of tourism, Grussaí (more impacted) and Manguinhos (less impacted), during periods of high and low tourism activity. The macrofauna of urbanized (U) and non‐urbanized (NU) sectors of the inter‐tidal zone was sampled and the number of visitors was recorded. General linear models revealed a decreasing in abundance of macrofauna species in the urbanized sectors of analyzed beaches, which are exposed to higher trampling impact than in non‐urbanized areas. At Manguinhos Beach, trampling did not affect the macrofauna (<1 visitors ? m^?²), except for the polychaete Scolelepis sp., which was less abundant in the U sector. Considering the benthic community, Atlantorchestoidea brasiliensis, Hemipodia californiensis and Scolelepis sp. were more sensitive to human trampling pressure and may be used as potential bioindicators of tourism impact. Management plans should consider mitigation of the effects of tourism, such as the control of the visitor number and their decentralization.     

A high-resolution Holocene record on the Southern Brazilian shelf: Paleoenvironmental implications

A high-resolution, multi-proxy record has been used to determine the environmental changes during the Holocene on the southern Brazilian shelf. Present oceanographic conditions reveal wind and freshwater input as the determinants of short-term productivity changes in the study area. Magnetic susceptibility and grain-size variations, together with proxies of productivity (organic carbon, carbon accumulation rate, Ba, Sr, and Ca content, Ba/Al, Ba/Ti, and Al/Ti ratios) were analyzed and compared with proxies of redox condition (V/Ti ratio), terrigenous input (Fe/Ca and Ti/Ca ratios), as well as other Element/Ti ratios, to evaluate the paleoceanographic and paleoclimatic changes over the period.The core covers a time interval of about 7650 years, with sedimentation rates varying from 0.025 to 0.250 cm a⁻¹, which represent time intervals of between 8 and 80 a per sample. There is a clear change in the sedimentation rate at about 2800 B.P.All grain-size and elemental results indicate the occurrence of conspicuous changes between 5200 and 5000 cal. B.P., as well as between 3000 and 2800 cal. B.P. A comparison of the results with the palynological information available from the adjacent continental areas suggests that the sedimentary changes in this last interval may be correlated with the onset of modern climatic conditions in South America, and especially, with the onset of the Plata Plume Water, a water mass that carries cold, less saline waters towards the north. However, minor changes are observed at ca. 1500 B.P. and are correlated with an increase in the atmospheric humidity. Furthermore, a time-series analysis undertaken using several proxies indicated the occurrence of Sub-Milankovitch cycles, which may be compared with those reported worldwide.     

A complete dynamical ozone budget measured in the tropical marine boundary layer during PASE

The Pacific Atmospheric Sulfur Experiment (PASE) was a field mission that took place aboard the NCAR C-130 airborne laboratory over the equatorial Pacific Ocean near Christmas Island (Kirimati, Republic of Kiribati) during August?CSeptember, 2007. Eddy covariance measurements of the ozone fluxes at various altitudes above the ocean surface, along with simultaneous mapping of the horizontal gradients provided a unique opportunity to observe all of the dynamical components of the ozone budget in this remote marine environment. The results of six daytime and two sunrise flights indicate that vertical transport into the marine boundary layer from above and horizontal advection by the tradewinds are both important source terms, while photochemical destruction consisting of 82% photolysis (leading to OH production), 11% reaction with HO₂, and 7% reaction with OH provides the main sink. The overall photochemical lifetime of ozone in the marine boundary layer was found to be 6.5 days. Ocean uptake of ozone was observed to be fairly slow (mean deposition velocity of 0.024?±?0.014 cm s^?1) accounting for a diurnally averaged loss rate that was ??30% as large as the net photochemical destruction. From the measurement of deposition velocity an ozone reactivity of ??50 s^?1 in seawater is inferred. Due to the unprecedented measurement accuracy of the dynamical budget terms, unobserved photochemistry was able to be deduced, leading to the conclusion that 3.9?±?3.0 ppt (parts per trillion by volume) of NO is present on average in the daytime tropical marine boundary layer, broadly consistent with several previous studies in similar environments. It is estimated, however, that each ppt of BrO hypothetically present would counter each ppt of NO above the requisite 3.9 ppt needed for budget closure. The long-term budget of ozone is further analyzed in the buffer layer, between the boundary layer and free troposphere, and used to derive an entrainment velocity across the trade wind inversion of 0.51 ± 0.38 cm s^?1.     

A Numerical Study of the Impact of Greenhouse Gases on the South Atlantic Ocean Climatology

The National Center for Atmospheric Research Community Climate SystemModel (NCAR CCSM, version 3) numerical coupled model is used tounderstand the climatic impacts on the South Atlantic Ocean due toindustrialization and consequent increase of greenhouse gasemission. Two experiments are analyzed: the first one withtrace/greenhouse gases at pre-industrial levels and a second one wherepresent day levels were adopted. The results show that the annualaveraged sea surface temperature, sea level pressure and barotropictransport intensify and precipitation weakens from one period to thenext. With respect to the seasonal cycle, the sea surface temperaturewarms relative to the pre-industrial period mainly during the winterand spring; while sea level pressure presents higher values in summerand autumn. Barotropic transport has revealed significant differencesbetween the two experiments at middle and high latitudes. Increasedtransport is associated with the intensification of the SubtropicalGyre and the Antarctic Circumpolar Current. Changes in barotropictransport and sea surface temperature leads to an intensification ofthe Polar Front and associated gradients. Examination of theprecipitation field differences showed an increase over the Amazonregion and along the South Atlantic Convergence Zone, during summer.The changes in sea surface temperature, sea-level pressure andbarotropic transport from the pre-industrial period to the present daywere more pronounced at high latitudes. These reach almost 1 °Cand 11Sv between 45-60° S, respectively. Majordifferences in precipitation are confined to the tropics.     

Pacific tropical–extratropical thermocline water mass exchanges in the NCAR Coupled Climate System Model v.3

In this study we document how model biases in extratropical surface wind and precipitation, due to ocean–atmosphere coupling, are communicated to the equatorial Pacific thermocline through Pacific Subtropical Cell (STC) pathways. We compare the simulation of climate mean Pacific Subtropical Cells (STCs) in the NCAR Community Climate System Model version 3 (CCSM3) to observations and to an uncoupled ocean simulation (the ocean component of the CCSM3 forced by observed wind stress and surface fluxes). We use two versions of the CCSM3 with atmospheric resolution of 2.8° (T42) and 1.4° (T85) to investigate whether the climate mean STCs are sensitive to the resolution of the atmospheric model.Since STCs provide water that maintains the equatorial thermocline, we first document biases in equatorial temperature and salinity fields. We then investigate to what extent these biases are due to the simulation of extratropical–tropical water mass exchanges in the coupled models. We demonstrate that the coupled models’ cold and fresh bias in the equatorial thermocline is due to the subduction of significantly fresher and colder water in the South Pacific. This freshening is due to too much precipitation in the South Pacific Convergence Zone. Lagrangian trajectories of water that flows to the equatorial thermocline are calculated to demonstrate that the anomalously large potential vorticity barriers in the coupled simulations in both the North and South Pacific prevent water in the lower thermocline from reaching the equator. The equatorial thermocline is shown to be primarily maintained by water that subducts in the subtropical South Pacific in both the coupled and uncoupled simulations. It is shown that the zonally integrated transport convergence at the equator in the subsurface branch of the climate mean STCs is well simulated in the uncoupled ocean model. However, coupling reduces the net equatorward pycnocline transport by 4 Sv at 9°S and 1 Sv at 9°N. An increase in the atmospheric resolution from T42 to T85 results in more realistic equatorial trades and off-equatorial convergence zones.     

Synergistic effect of extreme climatic events and urbanization on population density of the ghost crab Ocypode quadrata (Fabricius, 1787)

The combined effects of urbanization and extreme climatic events were examined on the ghost crab Ocypode quadrata, a well‐recognized ecological indicator in sandy beaches. The effect of storm waves was assessed before and after these climate events in beaches with different levels of urbanization in the coast of Brazil, Tropical Atlantic Ocean. The number of burrows was used as a metric for the population size of O. quadrata and the number of humans along the beaches as a proxy for the urbanization level. Significant differences were recorded in this species’ population density according to the human pressure. Our core modelling approach showed that the number of O. quadrata burrows was lower after storm waves in urbanized zones, compared to non‐urbanized ones. The interaction between storm waves and urbanization impacted the number of O. quadrata burrows negatively, and suggest that species’ populations are more vulnerable to the combined effects of extreme climatic events and urbanization. Extreme events are predicted to increase in frequency in the next few decades, and may modify or impair ecosystem functioning in sandy beaches by reducing populations of the O. quadrata, an important beach scavenger, which markedly contribute to the flux of energy in coastal trophic webs.