Spatial and temporal variations in pH and total alkalinity at the beginning of the rainy season in the Changjiang Estuary, China

The results of field observation carried out in May 2003 were used to examine pH and total alkalinity behaviors in the Changjiang Estuary. It was showed that pH and total alkalinity took on clear spatial variations in values with the minima in the low salinity region. Like salinity, transect distributions of pH and total alkalinity （TA） in a downriver direction had a sharp gradient each. These gradients appeared in such a sequence that the TA gradient was earlier than salinity and pH gradients, and the salinity gradient was earlier than the pH gradient. These distribution characteristics seemed to be strongly influenced by the mixing process of freshwater and seawater, for both pH and total alkalinity had significant linear relationships with salinity and temperature. For pH, phytoplankton activities also had a significant impact upon its spatial distribution. During a period of 48 h, pH and total alkalinity changed within wide ranges for every layer of the two anchor stations, namely, Stas 13 and 20, which were located at the mixed water mass and seawater mass, respectively. For both Stas 13 and 20, pH and TA fluctuation of every layer could be very wide during a 4 h period. As a whole, the data of the two anchor stations showed that neither variations in salinity and temperature nor phytoplankton activities were the main factors strongly influencing the total alkalinity temporal variability on a small time scale. The data of Sta. 20 implied that both salinity variation and phytoplankton activities had a significant influence on pH temporal variability, but the same conclusion could not be drawn from the data of Sta. 13.

Summertime freshwater fractions in the surface water of the western Arctic Ocean evaluated from total alkalinity

As a quasi-conservative tracer, measures of total alkalinity （TA） can be utilized to trace the relative fractions of freshwater and seawater. In this study, based on the TA and related data collected during the third Chinese National Arctic Research Expedition （JulySeptember 2008, 3rd CHINARE-Arctic） and the fourth Chinese National Arctic Research Expedition （JulySeptember 2010, 4th CH1NARE-Arctic）, fractions of sea-ice meltwater, river runoff, and seawater within the surface water of the western Arctic Ocean were determined using salinil~~ and TA relationships. The largest fraction of seeL-ice meltwater was found around 75~N within the Canada Basin during both surveys, which is located at the ice edge. Generally, it was found that the frac- tion of river runoff was less than that of sea-ice meltwater. The river runoff, composed mainly of contributions from the Yukon River carried by Bering inflow water and the Mackenzie River, was influenced by the currents, leading to two peak areas of its fraction. Our results show that the dilution effect of freshwater carried by Bering inflow water during the 3rd CH1NARE-Arctic in 2008 expedition period may be stronger than that during the 4th CH1NARE-Arctic in 2010 expedition period. The peak area of sea-ice meltwater fraction during the 4th CH1NARE-Arctic was different from that of the 3rd CHINAR-E-Arctic, corresponding to their sea-ice condition.

Distributions of dissolved inorganic carbon and total alkalinity in the Western Arctic Ocean

The third Chinese National Arctic Research Expedition （3rd CHINARE-Arctic in 2008） was carried out from July to September 2008. During the survey, numerous sea water samples were taken for CO2 parameter measurement （including total alkalinity TA and total dissolved inorganic carbon DIC）.The distribution of COs parameters in the Western Arctic Ocean was determined, and the controlling factors are addressed. The ranges of summertime TA, normalized TA （nTA）, DIC and normalized DIC （nDIC） in the surface seawater were 1 757 2 229 umol.kg 1 2 383-2 722 umol.kg-1, 1 681 2 034 pmol.kg 1, 2 119--2 600 umol.kg-1, respectively. Because of dilution from ice meltwater, the surface TA and DIC concentrations were relatively low. TA in the upper 100 m to the south of 78°N had good correlation with salinity, showing a conservative behavior. The distribution followed the seawater-river mixing line at salinity 〉30, then followed the seawater mixing line （diluted by river water to salinity = 30） with the ice meltwater. The DIC distribution in the Chukchi Sea was dominated by biological production or respiration of organic matter, whereas conservative mixing dominated the mixed layer TA distribution in the ice-free Canada Basin.

The Contribution of Nutrients and Water Properties to the Carbonate System in Three Particular Areas of the Tropical Atlantic (NE-BRAZIL)

Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO2. This study was performed on particular tropical areas that present a different seasonal behaviour related to the carbon cycle observed in the late rainy season (July 2013). Understanding the CO2 drawdown and outgassing potential in these areas is needed to call attention to more long-term monitoring efforts and protect understudied tropical coastal systems more efficiently. This study is focused on nutrient values, hydrological data, biogeochemical carbon behaviour linked to the carbonate system and includes estimates of CO2 fluxes in three contrasting areas off the northeastern Brazilian shelf: 1) an urbanised estuary (Recife-REC), 2) a coastal Island (Itamaracá-ITA) and 3) an oceanic archipelago (Fernando de Noronha-FN). In general, REC acted as a source, while ITA and FN as carbon sinks. In ITA, despite the high DIC and Total Alkalinity observed (mean ~2360 μmol·kg-1), the sink is associated with an effective cascading of atmospheric CO2 associated with turbulent shallow waters coupled with biogenic removal of and precipitation of CaCO3 by coralline algae. FN acted as a sink, linked to minor decreases in Total Alkalinity (mean~2295 μmol·kg-1) influenced by ammonium-based primary production, nitrogen fixation and sporadic entrainment of nutrient rich waters in the upper thermocline. More studies in different western tropical Atlantic coastal systems can improve the knowledge of tropical shelf seas and their contribution to the ocean carbon budget under specific regional trophic regimes.

Estimates and Variability of the Air-Sea CO2 Fluxes in the Gulf of Guinea during the 2005-2007 Period

Measurements of CO2 parameters (i.e. Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC)) were made from June 2005 to September 2007 in six EGEE (“Etude de la circulation océanique et de savariabilitédans le Golfe de GuinEE”) cruises to better assess air-sea CO2 fluxes in the Gulf of Guinea (6°N - 10°S, 10°E - 10°W). Two empirical relationships TA-Salinity and DIC-Salinity-Temperature were established. These relationships were then used to estimate the monthly fugacity of CO2 (fCO2) and air-sea CO2 fluxes. The monthly mean flux of CO2 reaches 1.76 ± 0.82 mmol·m-2·d-1 (resp. 2.90 ± 1.45 mmol·m-2·d-1) at the north of the Equator (resp. at the South). The north-south gradient observed as the patterns of the air-sea CO2 fluxes was mainly driven by the oceanic fCO2. This gradient was due to the low values of the CO2 parameters flowing by the Guinea Current (6°N - 0°) from the west to the east while the air-sea CO2 fluxes increased in the south (10°S - 0). In the north, the climatology of Takahashi underestimated the CO2 fluxes in the Gulf of Guinea when comparing to the estimated fluxes. This was due to the north-south gradient, which did not well reproduce by the climatology of Takahashi.