[1] In November 2004, a regional climate change workshop was held in Guatemala with the goal of analyzing how climate extremes had changed in the region. Scientists from Central America and northern South America brought long-term daily temperature and precipitation time series from meteorological stations in their countries to the workshop. After undergoing careful quality control procedures and a homogeneity assessment, the data were used to calculate a suite of climate change indices over the period. Analysis of these indices reveals a general warming trend in the region. The occurrence of extreme warm maximum and minimum temperatures has increased while extremely cold temperature events have decreased. Precipitation indices, despite the large and expected spatial variability, indicate that although no significant increases in the total amount are found, rainfall events are intensifying and the contribution of wet and very wet days are enlarging. Temperature and precipitation indices were correlated with northern and equatorial Atlantic and Pacific Ocean sea surface temperatures. However, those indices having the largest significant trends (percentage of warm days, precipitation intensity, and contribution from very wet days) have low correlations to El Niño-Southern Oscillation. Additionally, precipitation indices show a higher correlation with tropical Atlantic sea surface temperatures.

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New geologic mapping, structural studies, and geochronology of Miocene volcanic and sedimentary rocks in the southern Sierra Juarez, Baja California, shed light on the extensional history of the Gulf Extensional Province prior to sea-floor spreading in the Gulf of California. The southern Sierra Juarez is underlain by lower-middle Miocene rocks including fluvial strata, intermediate composition volcanic deposits, basalt lava flows and cinder cones, and dacite pyroclastic deposits and lavas that nonconformably overlie the Cretaceous Peninsular Ranges batholith. The 40 Ar/ 39 Ar geochronology indicates that basaltic rocks are 16.90 ؎ 0.05 Ma and dacite pyroclastic deposits are between 16.69 ؎ 0.11 Ma and 15.98 ؎ 0.13 Ma. These strata were subsequently cut by two generations of faults. First generation faults comprise a dominant set of north-south-striking, west-dipping normal faults, a secondary set of north-south-striking, east-dipping normal faults, and a lesser set of variably oriented strike-slip faults. All three fault sets are temporally and spatially related and were produced by east-west extension. The dominant west-dipping faults, which are antithetic to and oblique to the east-dipping Main Gulf Escarpment, may have been a precursor or an early phase accommodation zone along the escarpment. West-dipping normal faults are cut by a 10.96 ؎ 0.05 Ma dacite hypabyssal intrusion, thus bracketing the age of east-west extension between 15.98 ؎ 0.13 Ma and 10.96 ؎ 0.05 Ma. Hence, this faulting event clearly indicates a period of extension that predates the onset of oceanic rifting and even predates other dated Miocene extension within Baja California. Second generation faults, which are comprised of east-west-striking strike-slip faults that cut first generation faults and associated northwest-striking, northeastdipping normal faults, may be related to early development of the Transpeninsular Strike-slip Province. Global plate reconstructions suggest that transtensional motion between the North American and Pacific plates along the western margin of Baja California began during middle Miocene time, coeval with east-west extension in the southern Sierra Juarez. This observation supports a hypothesis that middle Miocene transtensional plate motion was partitioned into two components: a strike-slip component parallel to active faults along the western offshore margin of Baja California, and an extensional component normal to the margin, but located in what is now the Gulf Extensional Province. Hence, the onset of extension within the circum-gulf region was in response to plate boundary processes.

The seasonal variability of bio‐optical and physical properties within the upper ocean at a site in the Sargasso Sea (34°N, 70°W) has been observed using multivariable moored systems (MVMS) during a 9‐month period (March through November 1987). In addition, complementary meteorological data, sea surface height (Geosat) and sea surface temperature maps, and expendable bathythermograph (XBT) and shipboard profile data (physical and bio‐optical) have been utilized for interpretation. The observations during March are characteristic of late wintertime conditions of a deep isothermal layer (∼18–19°C), but with intervening periods of warming due to the advection of warm outbreak waters associated with Gulf Stream meanders. The mixed layer depth shoals from greater than 160 m to about 25 m in late March (spring transition). Phytoplankton blooms follow the mixed layer shoaling. A succession of phytoplankton populations occurs during this transitional interval. Mesoscale variability associated with cold core rings and warm outbreak waters associated with the Gulf Stream are evident at various times. The mixed layer remains near 25 m for the summer and deepens in mid‐September. A relatively intense subsurface maximum in chlorophyll develops at ∼75 m following the spring transition. The maximum persists, but weakens in mid‐summer. The present study clearly indicates that important processes associated with and contributing to the seasonal cycle occur on short time and space scales and that integrated data sets obtained from moorings, ships, and satellites can be used to effectively study bio‐optical and physical phenomena on time scales from minutes to seasons.