Ocean acidification (OA) is expected to reduce the calcification rates of marine organisms, yet we have little understanding of how OA will manifest within dynamic, real-world systems. Natural CO₂, alkalinity, and salinity gradients can significantly alter local carbonate chemistry, and thereby create a range of susceptibility for different ecosystems to OA. As such, there is a need to characterize this natural variability of seawater carbonate chemistry, especially within coastal ecosystems. Since 2009, carbonate chemistry data have been collected on the Florida Reef Tract (FRT). During periods of heightened productivity, there is a net uptake of total CO₂ (TCO₂) which increases aragonite saturation state (Ω_arag) values on inshore patch reefs of the upper FRT. These waters can exhibit greater Ω_arag than what has been modeled for the tropical surface ocean during preindustrial times, with mean (± std. error) Ω_arag-values in spring = 4.69 (±0.101). Conversely, Ω_arag-values on offshore reefs generally represent oceanic carbonate chemistries consistent with present day tropical surface ocean conditions. This gradient is opposite from what has been reported for other reef environments. We hypothesize this pattern is caused by the photosynthetic uptake of TCO₂ mainly by seagrasses and, to a lesser extent, macroalgae in the inshore waters of the FRT. These inshore reef habitats are therefore potential acidification refugia that are defined not only in a spatial sense, but also in time; coinciding with seasonal productivity dynamics. Coral reefs located within or immediately downstream of seagrass beds may find refuge from OA.

A coherent plume from the Mississippi River was detected in MODIS imagery in July–October 2004 extending from the eastern Gulf of Mexico into the Florida Straits (FS), and reaching the Gulf Stream (GS) off Georgia. The plume was sampled from ships in the FS and the GS. In early August, the plume was about 10–20 km wide in the western FS and about 50 km wide off Georgia. The FS ship survey (16–26 August) documented a 50 km, 10–20 m deep band with anomalies in surface salinity (−0.8), temperature (0.5°C), and surface chlorophyll concentration (2×) relative to FS waters outside the plume. Nutrient concentrations were only slightly higher in the FS plume and there was no apparent increase in colored dissolved organic matter. We estimate that the plume carried some 23% (∼2778 m³ s⁻¹) of the Mississippi River discharge between July and September 2004 into the GS.

Average cross sections of downstream velocity and temperature, obtained using PEGASUS current profiles at three locations along the Gulf Stream, have been partitioned into 2.5°C temperature intervals to examine the distribution of transport increase versus temperature between the two southern sections (27° and 29°N) and off Cape Hatters(73°W). Between 27° and 29°N the total transport of the Florida Current over the sections increased only by about 3 × 106 m3 s−1 (3 Sv) but the current broadens by about 50%. By Cape Hatteras, the transport has increased nearly three-fold to 93.7 Sv, of which two-thirds of the increase is contained in the 19.5°–17.0°C (“18°”) layer and in water colder than the 7°C “still” temperature found at 27°N. Cross-stream distributions of layer transport, potential vorticity, and thickness are estimated. At each section, the 10 × 10−7 m−1 s−1 contour tends to be a boundary (independent of temperature) between the region of relatively uniform layer potential vorticity on the a... Abstract Average cross sections of downstream velocity and temperature, obtained using PEGASUS current profiles at three locations along the Gulf Stream, have been partitioned into 2.5°C temperature intervals to examine the distribution of transport increase versus temperature between the two southern sections (27° and 29°N) and off Cape Hatters(73°W). Between 27° and 29°N the total transport of the Florida Current over the sections increased only by about 3 × 106 m3 s−1 (3 Sv) but the current broadens by about 50%. By Cape Hatteras, the transport has increased nearly three-fold to 93.7 Sv, of which two-thirds of the increase is contained in the 19.5°–17.0°C (“18°”) layer and in water colder than the 7°C “still” temperature found at 27°N. Cross-stream distributions of layer transport, potential vorticity, and thickness are estimated. At each section, the 10 × 10−7 m−1 s−1 contour tends to be a boundary (independent of temperature) between the region of relatively uniform layer potential vorticity on the a...