No abstract

Fresh submarine groundwater discharge (FSGD), a well-established land-to-sea pathway for water and materials, has increased (∼30%) along the midlatitude coast of Japan with the shift from snowfall to rainfall since the 1980s. The terrestrial-derived FSGD in this area has a residence time of 10−20 years, and its material flux may respond quickly to the effects of recent warming. In this study, FSGD collected directly from the seafloor (∼10 m water depth) during two different periods (2017−2021 and 2001−2003) was observed using the same consistent method to evaluate the warming-related effects on FSGD material fluxes. In the FSGD system, dissolved constituents and the isotopic composition decreased by 10−30% and residence time by one-third compared to the previous data, even though homogeneous water quality was maintained among the FSGD-connected aquifers for each period. Most concerning is that these changes resulted in a drop in pH and an increase in FSGD-derived carbon flux. Total nutrient fluxes from land have roughly halved, resulting in lower primary productivity and an estimated doubling of excess dissolved inorganic carbon in coastal waters. Our findings present direct evidence of the sensitivity of carbon flux to climate change and the urgency for carbon-related FSGD research worldwide.

No abstract

Spectrophotometry using a small sample volume has been developed to measure the alkalinity (or bicarbonate). However, the experimental and calculation processes are complicated, and the atmospheric CO 2 has to consider in preparing standard solutions. This study aims to quantify the dissolution of the atmospheric CO 2 when using spectrophotometry. Also, the effect on the standard solution in titrating that uses to make calibration curve are calculated to understand the effects of the different CO 2 concentrations in a laboratory. The difference between the bicarbonate concentrations and the calculated ones based on the updated chemical equilibrium formula was from 0.038 to 5.4×10 -6 mg/L. The maximum difference was found at pH 5.0 in the 10 mg/L HCO 3standard solutions. The bicarbonate concentration without the atmospheric CO 2 reaction (C1) and with the atmospheric CO 2 reaction (C2) was calculated by the PHREEQC. The difference between C1 and C2 ranged from 0.01 to 0.02 mg/L, but the calculated bicarbonate concentrations between the HCl titration and the PHREEQC output were certainly different, which ranged from 3.1 to 11.5 mg/L at the pH 4.3 endpoint. In contrast, at the pH 4.8 endpoint, the difference was significantly decreased from 0.8 to 1.3 mg/L. The effect of the increasing atmospheric CO 2 by human breathing in a laboratory is only 0.05 mg/L in the standard solutions when titrating. From the results of this study, the experimental and calculation processes to correct the bicarbonate concentration by the effect of the atmospheric CO 2 in a laboratory may be omitted if natural waters are targeted. Hosted fileessoar.10512060.1.docx available at https://authorea.com/users/555916/articles/606236-ananalytical-approach-for-alkalinity-measurement-with-a-small-volume-of-natural-water-bychemical-equilibrium-formula-and-geochemical-modeling An analytical approach for alkalinity measurement with a small volume of natural water by chemical equilibrium formula and geochemical modeling

Fresh Submarine Groundwater Discharge (FSGD) is an important pathway for the transport of water and materials from land to ocean, but changes in the transport may occur as snowfall decreases. This study was conducted on Japan's mid-latitude western coast where FSDG is a quarter of the total riverine discharge and snowfall has decreased by ˜50% since the 1990s. The altitude of the FSGD recharge area in 2018 has shifted 100-150 m higher than that in 2000, and the water residence time has decreased from 4-15 to 3-11 years. The pH of the groundwater dropped by 0.5, its CO (aq) concentration doubled, and nitrogen and phosphorus decreased by 30-40% and 70-80%, respectively. These changes in nutrients reduced primary productivity in coastal waters and doubled the excess dissolved inorganic carbon flux. Our evidence highlights the sensitivity of FSGD carbon flux to climate change and of the urgency of carbon-related FSGD research worldwide.