CO2 Consumption Rates in the Glacierized Himalayan Headwaters: The Importance of Sulfuric and Nitric Acid‐Mediated Chemical Weathering Reactions in Geologic Carbon Cycle

Silicate and carbonate weathering reactions consume atmospheric CO2 depending on the type of weathering agents, namely carbonic (H2CO3), sulfuric (H2SO4), and nitric acids (HNO3), and have potential climate implications. However, the importance of HNO3 in weathering processes in the Himalayan glacierized basins has not been examined yet but is critical to better constrain the concomitant short (<103 years) and long‐term (>106 years) variability in the carbon cycle as it can drive negative feedback to a climate. By analyzing time‐series hydro‐geochemical data of proglacial meltwater in the Ganga headwaters of Central Himalaya, we demonstrate that the weathering rate of carbonate minerals is increased 1.06 times when the role of HNO3 is considered together with H2CO3 and H2SO4 in comparison to the role of H2CO3 and H2SO4. However, we also observe that the CO2 drawdown rate decreases 1.13 times and 1.06 times when the role of all three acids is considered in silicate and carbonate weathering reactions, respectively, compared to the CO2 drawdown rates linked to the role of H2CO3 and H2SO4. Moreover, the involvement of HNO3 in chemical weathering can reduce the inorganic global carbon sink by releasing CO2 into the ocean‐atmosphere system. We conclude that HNO3‐mediated chemical weathering reactions are important processes that alter the geologic carbon cycle of high‐altitude glacierized Himalayan catchments as well as on a global scale.


Major Ions and Dissolved Silica Analysis
The samples were used for the measurement of dissolved major ions and silica concentrations. All the ions (F − , Cl − , NO3 − , SO4 2− , K + , Na + , Ca 2+ , and Mg 2+ ) were measured by ion chromatography (930 Compact IC Flex, Metrohm) with a resolution of 0.01 mg L −1 . Calibration standards for anion and cation analysis were prepared using Multi-element Ion Chromatography Anion Standard solution and Multi-element Ion Chromatography Cation standard solution with a certified molar concentration of 10.0 mg kg −1 ±0.2% for each anion and cation. A 10-point Calibration curve was established by plotting peak areas for each ion against the concentration with the range from 0.1 to 10 mg L −1 . The correlation coefficient of the calibration curve was r 2 ≥ 0.995. One mg L −1 standard solution was analyzed repeatedly after each tenth sample for accuracy check. Overall accuracy for all the cations is between 0.5% and 2% with relative standard deviation ranging from 0.03 to 0.18 mg L −1 . Alkalinity was measured by titration technique within 12 hr of sample collection using sulfuric acid of 0.01639 N as the titrant. The normality of the titrant was tested using a standard solution of sodium carbonate of 0.01639 N. Uncertainty of the alkalinity test was estimated as ±0.04 meq L −1 . As the pH of the river water falls between 7.04 and 8.30, in this study, HCO3 − is considered equivalent to the alkalinity of meltwater.
Dissolved silica concentrations were determined by UV-VIS-NIR-Spectroscopy using the heteropoly blue method (Baird et al., 2017). In this method, the concentration of dissolved silica was determined using a light absorbance value, the concentration of a standard, and path length following Beer-Lamberts law. The resolution of the method was approximately 50 μg L −1 SiO 2 , which can be detected spectro-photometrically with a 1 cm light path at 815 nm. Here, Sodium metasilicate nonahydrate (Na 2 SiO 3 .9H 2 O) is used as the calibration standard, and calibration standard solutions were prepared in the range of 10-120 μmol L −1 . Using the absorption values of each calibration standard, a calibration curve was established against the concentration of calibration standards. The correlation coefficient of the calibration curve was calculated to be r 2 ≥ 0.995. Each standard was analyzed 3 times for accuracy check and the overall accuracy of the measurement is within 5%.

Forward Model for Source Apportionment of Solutes
To estimate the relative contribution of different source end members, a forward model is used (Deuerling et al., 2019;Galy & France-Lanord, 1999;Moon et al., 2007). Input from anthropogenic activities to the river is ignored in this study as the sampling site is near the snout of the glacier without any human settlements. The dissolved solutes in meltwater are considered to be a mixture of atmospheric input, dissolution of evaporite minerals, chemical weathering of silicate and carbonate rocks, and oxidation of pyrite. So for any element (X), the mass budget equation can be written as follows: [X]meltwater = Xatm + Xevap + Xsil + Xcarb + Xpyr (1) where Xatm, Xevap, Xsil, Xcarb , and Xpyr denote the proportion of major ions from atmospheric, evaporite, chemical weathering of silicate and carbonate, and sulfide oxidation, respectively. Contributions from atmospheric, evaporite dissolution, chemical weathering of silicate and carbonate, and pyrite oxidation are calculated using the following procedures.
However, in glacierized regions, the atmospheric contribution also comes from ice meltwater and snow meltwater. Since ice and snow meltwater are major contributors to proglacial meltwater, ion concentrations in ice meltwater, snow meltwater, and rainwater are used for atmospheric correction in this study using the following equation : where Xatm refers to the corrected concentration of any element derived from atmospheric deposition, Xice+snow refers to the average ionic concentration in glacier snow meltwater and ice meltwater, and Xref refers to ionic concentration derived from rainfall. Xref is calculated using the weighted average ionic content of rainwater Xavg , and concentration factor F, that is, Xref = F × Xavg . F is the coefficient of evapotranspiration and can be calculated using the following equation : P is the total rainfall (mm y −1 ) and R is the runoff (mm y −1 ) in the glacierized basin. During the study period of June to mid-October of 2019, the total discharge in the Mandakini River was 8.59 × 10 2 m 3 s −1 . The total calculated runoff is 6,089 mm using a basin area of 12.2 km 2 and the amount of total rainfall in the same period is 665 mm. Hence, the value of F can be calculated as 0.11. Atmospheric input for all the major ions was calculated using Equation 3.
For the calculation of evaporite contribution, we have considered the presence of evaporite in our study area based on the previous studies conducted in the Higher Himalayan regions (Chakrapani, 2005;Krishnaswami & Singh, 1998). Here we assume that evaporite dissolution mostly contributes Cl − , SO4 2− , Na + , K + , and Ca 2+ and therefore we tried to quantify the contributions of evaporite dissolution in meltwater. For example, we considered Cl − to be derived from atmospheric and evaporite deposits. The amount of Cl − sourced from evaporite deposition is calculated as the difference between the total measured Cl − in the river and the calculated Cl − from atmospheric deposition. To calculate the contribution of SO4 2− from evaporite, mineral dissolution stoichiometries are used. Since evaporite deposits are mainly composed of halite (NaCl), sylvite (KCl), and gypsum (CaSO 4 .(H 2 O)), Cl normalized ratio is used to estimate evaporite contribution following Torres et al. (2017).
In evaporite deposits such as halite (NaCl) and sylvite (KCl), both Na + and K + are present in a 1:1 ratio with Cl − which is used to calculate Na + and K + contribution from evaporite deposits. On the other hand, both SO4 2− and Cl − are present in a 1:1 ratio with Ca 2+ and Na + in gypsum and halite. Here we have considered that the halite, sylvite, and gypsum deposits are pure and unaltered, and have suffered the same degree of dissolution that produce Na + /Cl − , K + /Cl − , and Ca 2+ /SO 4 2− in a 1:1 ratio, respectively. Thus, considering SO4 2− /Cl − and Ca 2+ / Cl − ratios as 1:1, the contributions of Ca 2+ , SO4 2− as well as Na + and K + from evaporite mineral dissolution are calculated.
Apart from atmospheric precipitation and evaporite dissolution, the remaining Na + and K + are mainly derived from SWR, whereas Ca 2+ and Mg 2+ are derived from weathering of both silicate and carbonate rocks. Silicate weathering inputs for Na + and K + are determined as the remaining concentration in meltwater after the correction for atmospheric and evaporite depositions (Equations 5 and 6). Ca 2+ and Mg 2+ sourced from weathering of silicates are calculated using the molar ratio of (Ca/Na) sil and (Mg/Na) sil released from silicate rocks during chemical weathering. In this study, values of 0.7 ± 0.3 and 0.3 ± 0.2 for (Ca/Na) sil and (Mg/Na) sil (Krishnaswami & Singh, 1998)

Chemical Weathering and Associated CO 2 Consumption Rates Calculations
Here, it is assumed that the ratios of silicate and carbonate rocks weathered by H 2 SO 4 and HNO 3 acid are same as those by H 2 CO 3 (Galy & France-Lanord, 1999;C. Li & Ji, 2016). Therefore we calculate the proportion of HCO3 − coming from H 2 SO 4 -mediated carbonate weathering ( (HCO − 3 ) cw sulf uric ) by the following equations (C. Li & Ji, 2016):  (Han & Liu, 2004;C. Li & Ji, 2016). In the present study, the average molar ratio of (Ca)carb∕(Mg)carb is 4.6 and the average molecular formula of carbonate is derived as Ca 0.82 Mg 0.18 CO 3 . Therefore, The rate of SWR is calculated based on S. Roy et al. (1999).
where ( The calculation of the CO 2 consumption rate by SWR depends on the amount of total cationic charge derived from SWR and the amount of sulfate and nitrate resulting from SWR caused by H 2 SO 4 and HNO 3 . Here 2 ( ) sw nitric represent the total cationic charge (Na + + K + + 2Ca 2+ + 2Mg 2+ ) derived from H 2 SO 4 -induced SWR and HNO 3 induced SWR. Silicate weathering causes consumption of atmospheric CO 2 only when it is weathered by H 2 CO 3 , while SWR by H 2 SO 4 and HNO 3 does not cause any atmospheric CO 2 sequestration. Thus, the total cationic charge derived from SWR caused by H 2 SO 4 and HNO 3 needs to be considered while calculating the CO 2 consumption rate by SWR to avoid overestimation of CO 2 flux (Lerman & Wu, 2006;Moon et al., 2007;Ryu et al., 2008;Spence & Telmer, 2005). Equation 29 can be modified accordingly to calculate CO 2 flux by SWR when (a) H 2 CO 3 and H 2 SO 4 are weathering agents and (b) H 2 CO 3 is the only weathering agent.

Calculations of Inorganic CO 2 Balance Over Geological Timescales
The impact of chemical weathering on the sequestration or release of CO 2 was estimated by considering the balance between alkalinity and dissolved inorganic carbon (DIC) produced by weathering (Bufe et al., 2021). The generation of alkalinity and DIC depends on the reactions that supply protons to drive chemical reactions, and which mineral phases consume protons and release alkaline earth cations. Here, we consider that protons are coming from the dissociation of H 2 CO 3 , H 2 SO 4 , and HNO 3 , which cause weathering of silicate and carbonate rocks. The relative proportions of alkalinity and DIC generation by each chemical weathering are quantified by writing the relevant half-reactions and then combining them to yield full reactions for chemical weathering of silicates and carbonates by H 2 SO 4 and H 2 CO 3 following Torres et al. (2016Torres et al. ( , 2017. Similarly, we have calculated alkalinity and DIC generation for HNO 3 -induced carbonate and SWR. See Supporting Information S1 for the detailed calculations of alkalinity and DIC generated due to individual weathering reactions. The effect of chemical weathering on inorganic CO 2 balance for a time scale shorter than carbonate precipitation (<10 ky) can be calculated after modifying the equation by Bufe et al. (2021): where [CO2] st are the moles of CO 2 produced (positive [CO2] ) or consumed (negative [CO2] ) per unit volume of weathering fluid for short-term (st). Here [Cat] eq carb is the equivalent concentration of total cations coming from weathering of carbonate minerals. The fraction of cation charge balanced by sulfate, fsulf , and by nitrate, fnitrate are defined as: For geologic timescales longer than calcium carbonate compensation time (10 ky), the generation of alkalinity and dissolved cations due to chemical weathering is balanced by the precipitation of marine calcium carbonate. The medium-term (mt) effect of chemical weathering on inorganic CO 2 balance for a time scale longer than carbonate precipitation (>10 ky) can be calculated as follows: It is important to mention that in the above scenarios, alkalinity generation by sulfide reduction (Jørgensen, 1982) or alkalinity consumption by reverse weathering reaction (Garrels, 1965) is not taken into account (Bufe et al., 2021). For a long-term (lt) timescale spanning millions of years, the inorganic CO 2 balance could possibly be determined by the amount of calcium produced through SWR (Bufe et al., 2021): 10.1029/2023GC010919 8 of 21 ] eq sil is the equivalent concentration of calcium from SWR. This calculation is valid only when a system maintains a constant boundary system and steady-state carbon cycle.

Temporal Variations of Geochemical Parameters
Temporal variations in the measured geochemical parameters are reported in Table 1 and shown in Figure 2. The major ion compositions of rainwater, snow, and ice samples are listed in Table S1 in Supporting Information S1. All the meltwater samples are mildly basic with average pH values of 7.67 ± 0.33 (n = 7, range: 7.46-8.30) during the pre-monsoon season (June), 7.74 ± 0.27 (n = 12, range: 7.16-8.30) in monsoon season (July-August), and 7.71 ± 0.48 (n = 14, range: 7.04-8.20) in the post-monsoon season (September-October).
The charge balance error (CBR = [(TZ + − TZ − )/(TZ + + TZ − ] × 100%) of the meltwater samples for the ablation season of 2019 was mostly below 10%. The charge balance error above 10% can be attributed to the measurement technique of HCO3 − by the alkalinity test method. Concentrations of major cations in the meltwater follow an order of Ca 2+ > Mg 2+ > Na + > K + . Calcium is the most dominant cation with an average concentration range from 102 to 303 μmol L −1 . Bicarbonate is the dominant anion with concentration ranges from 131 to 287 μmol L −1 , followed by SO4 2− with concentration varies from 45 to 192 μmol L −1 and then NO3 − and Cl − respectively. Major ion concentrations in river water show notable fluctuation throughout the ablation season ( Figure 2). Specifically, the concentration of NO3 − in water is substantially higher during the pre-monsoon period with an average value of 50 μmol L −1 , followed by a sharp decrease during the monsoon period with an average concentration of 19 μmol L −1 , and again increase in the post-monsoon season with an average value of 27 μmol L −1 . In contrast, Cl − , SO4 2− , and cations such as K + , Na + , Ca 2+ , and Mg 2+ show relatively consistent concentrations between the monsoon and pre-monsoon periods. However, the concentration of these ions increases significantly during the post-monsoon period.
The chemical weathering regimes of meltwater discharge and the relationship between meltwater composition and rock types are evaluated by plotting the concentrations of major ions in the Tri-linear and ternary diagram in Figure S1 in Supporting Information S1. The Piper plot shows that the percentage value of alkaline earth metals (Ca +2 + Mg +2 ) is considerably higher (80%-90%) than the alkalis (Na + + K + ) (10%-20%). On the other hand, meltwater samples are distributed along the HCO3 − axis with a 60%-80% value of SO4 2− , followed by (NO 3 − + Cl − ). From the Piper plot, it is clear that Ca 2+ is significantly higher than other cations (Mg 2+ , Na + , K + ), whereas the percentage of (SO 4 2− + NO3 − + Cl − ) ranges from 60% to 80% with 15%-30% HCO3 − . Meltwater samples are plotted along the (SO 4 2− + Cl − + NO3 − ) axis with a higher contribution of HCO3 − and dissolved Si of 40%-65%.
The input of SWR accounted highest for K + with 88%, followed by 76% for Na + , 53% for Ca 2+ , and 23% for Mg 2+ , whereas 32% of Ca 2+ and 63% of Mg 2+ are contributed by carbonate minerals. Temporal variations in the sources of individual ions are reported in Table S2 in Supporting Information S1. The relative source contributions of the solutes to the meltwater are shown in Figure 3. The contribution of various sources to the riverine solute does not exhibit significant variation except the atmospheric contribution, which shows a decrease of 20%-23% during 10.1029/2023GC010919 9 of 21  the monsoon and post-monsoon period compared to the pre-monsoon period. On the other hand, the average contributions from silicate and carbonate weathering were (38 ± 3)% and (20 ± 2)% with differences of 2%-4% and 4%-6% between monsoon and non-monsoon seasons, respectively. Contribution from sulfide oxidation and evaporite dissolution accounted for an average of (24 ± 3)% and (9 ± 0.4)% throughout the ablation season.

Source Identification of Dissolved Major Ions
Solute chemistry in river water is mainly influenced by natural processes and anthropogenic factors (Chakrapani, 2005;Dalai et al., 2002;Krishnaswami & Singh, 2005) such as atmospheric deposition, chemical weathering of bedrock materials, and anthropogenic inputs. Here we discuss the individual sources of major ions contributing to the meltwater.

Atmospheric Inputs
In the rainwater sample as well as in snow and ice samples, Na-normalized molar ratios of ionic concentrations show higher values compared to sea-salt composition (Table S3 in Supporting Information S1). Enrichment of SO4 2− and NO3 − in rainwater with respect to sea-salt points toward the significant anthropogenic emissions to the atmosphere and less contribution of sea-salt to the meltwater. Since HCO3 − concentration in rainwater is below the detection limit, the atmospheric contribution of bicarbonate ions to meltwater can be ignored (Xie et al., 2021).

−
Major anthropogenic sources such as agricultural inputs, sewage, and industrial discharge were absent in the study site. The only possible source of anthropogenic inputs is industrial emission in the form of atmospheric loading. Identification of SO4 2− and NO3 − sources is important in estimating CO 2 consumption rates as these ions can come from atmospheric acid deposition and can supply protons for weathering reactions. The possible sources of SO4 2− can be the dissolution of evaporite and the form of H 2 SO 4 coming from pyrite oxidation and atmospheric acid deposition. However, in the presence of evaporite, there would be a simultaneous increment of corresponding SO4 2− concentration. Dissolution of evaporite can also contribute Ca 2+ to river water apart from weathering of silicates and carbonates. Thus, the Ca 2+ normalized SO4 2− ratio in a sample can remove the influence of evaporite dissolution and the Ca 2+ normalized SO4 2− and Ca +2 normalized NO3 − ratios can be used to evaluate the origin of anthropogenic sources. A poor correlation between SO4 2− /Ca 2+ and NO3 − /Ca 2+ in meltwater samples indicates that both ions could have originated from different sources (Huang et al., 2017) (Figure S2 in Supporting Information S1). A higher SO4 2− /Na + ratio in river water compared to rainwater and 4% atmospheric contribution indicates other sources such as the dissolution of evaporite and sulfide oxidation are major contributing sources of sulfate in meltwater (C. Li & Ji, 2016;W. Liu et al., 2016). Atmospheric contribution of SO4 2− can be from sea salt and/or acid deposition. However, higher SO4 2− /Na + values in rainwater and as well as in snow and ice samples compared to sea-salt composition ( Table S3 in Supporting Information S1), it is considered that SO4 2− from atmospheric deposition is in the form of H 2 SO 4 acid deposition. The atmospheric input of NO3 − in meltwater accounted for 84% and significantly higher NO3 − /Na + ratio in rainwater and as well as in snow and ice samples compared to meltwater samples (Table S3 in Supporting Information S1) indicating that atmospheric deposition is one of the main sources of nitrate in meltwater. Since sea salt doesn't contain any NO3 − , the atmospheric NO3 − deposit is considered to be acid deposition. The rest of the nitrate in meltwater is assumed to be derived from the nitrification of supraglacial ammonia or oxidation of organic-rich debris (Freppaz et al., 2021;C. Li & Ji, 2016;Wynn et al., 2007).

Rock Weathering Inputs
Chemical weathering of bedrock materials is the major source of solutes to river water. There are two types of chemical reactions (Krishnaswami & Singh, 2005). (a) Dissolution reactions which are congruent dissolution of evaporite deposits such as NaCl → Na + + Cl − ; CaSO4 → Ca 2+ + SO 2− 4 . (b) Acid hydrolysis which requires protons (H + ) to cause chemical reactions (Raiswell, 1984).
Ca2SiO4(s) + 4H + (aq) = 2Ca 2+ (aq) + H4SiO4(aq) To calculate the rates of chemical weathering and CO 2 consumption, chemical reactions 34 and 35 are important as they require sources of protons which are exchanged for base cations from bedrock material. Table 2a shows the different sources of H + ions and the processes responsible for their generation. The most common source of aqueous protons is (a) H 2 CO 3 which is generated by the dissociation of dissolved CO 2 either directly from the atmosphere in rain or from soil gas in river waters. In areas like rugged mountains or glaciated regions where vegetation is sparse, atmospheric-derived CO 2 could be the dominant source of H 2 CO 3 (Krishnaswami & Singh, 2005). (b) The second source of protons is provided by H 2 SO 4 and can be generated by two processes: (i) oxidation of sulfides such as pyrite present in the bedrock of glaciers (Bufe et al., 2021;Torres et al., 2014) or (ii) the reaction between anthropogenic SO 2 from industrial emission in the atmosphere and the free radicals OH and/ or aqueous H 2 O 2 in droplets (Berner et al., 1983; S. L. Li et al., 2008). (c) Another additional source of protons can be HNO 3 which can be produced by (i) microbial oxidation of nitrogen compounds (nitrification) present in debris (Nitric Acid Manufacture, 1964) or (ii) reaction of oxides of nitrogen emitted into the atmosphere with the free radicals OH and/or aqueous H 2 O 2 in droplets just as sulfur dioxide (Mohnen, 1988). Weathering reactions of   Table 2b.

Role of Sulfuric and Nitric Acid in Rock Weathering
From the reactions mentioned in Table 2b it is clear that apart from H 2 CO 3 , strong acids such as H 2 SO 4 and HNO 3 can be sources of protons causing the weathering of silicate and carbonate rocks. In this study, it is assumed that total NO3 − in meltwater is derived in the form of HNO 3 from atmospheric deposition and nitrification of organic matter and participates in chemical weathering. For SO4 2− , it is considered that contributions from atmospheric deposition and pyrite oxidation are in the form of H 2 SO 4 and thus ] evaporite ) represents the amount of H 2 SO 4 participating in chemical weathering. For the calculation of rates of chemical weathering and CO 2 consumption, major ionic concentrations are corrected for other sources to have total cations derived from silicate and carbonate weathering (total cations* = [Na + * + K + * + Ca 2+ * + Mg 2+ *] silicate+carbonate ).
When chemical weathering is caused only by the H 2 CO 3 then the equivalent ratio of [total cations*/HCO 3 − ] should be 1 (total cations* = [Na + * + K + * + Ca 2+ * + Mg 2+ *] silicate+carbonate ) (Equations 8 and 11-14 in Table 2b). The relationship between total cations* and HCO3 − shows significant excess in total cations* concentration where the equivalent ratio of [total cations*/ HCO3 − ] ranges from 1.08 to 3.26 with a mean value of 1.9 ± 0.5 (n = 33). The higher equivalent ratio of [total cations*/HCO 3 − ] suggests that other weathering agents are required to balance the excess cations* (Figure 4a). Equations 8, 9 and 11-18 in Table 2b show that when carbonate and SWR is governed by H 2 CO 3 and H 2 SO 4 , the equivalent ratio of [total cations*/HCO NO3 − ] should be 1, and the regression correlation (R 2 ) should also be 1, with an intercept of 0 (He, 2021;Huang et al., 2017). Figures 4b and 4c show that the plots of the equivalent ratio of [total cations*/HCO 3 − + SO4 2− ] and [total cations*/ HCO3 − + SO4 2− + NO3 − ] both have a slope of the regression line close to 1. After considering NO3 − to compensate for total excess cations* the slope of the regression line changes from 0.8 to 0.9 and the correlation coefficient is changed from 0.5 to 0.6. A smaller change implies that NO3 − has some but limited impact on the chemical weathering of rocks (He, 2021). The plot of equivalent ratios [total cations*/HCO in Supporting Information S1) shows that meltwater samples are distributed between three end members: chemical weathering by carbonic acid, sulfuric acid, and nitric acid, which implies that chemical weathering of silicate and carbonate rocks is controlled by different contribution ratios of H 2 CO 3 , H 2 SO 4 , and HNO 3 (Xie et al., 2021). Moreover, according to Equations 9, 10, and 15-22 in Table 2b, the equivalent concentration of [total cations*] and [SO 4 2− + NO3 − ] will increase simultaneously if both H 2 SO 4 and HNO 3 are involved in weathering of silicates and carbonates (Huang et al., 2017;Xie et al., 2021). A positive correlation between the equivalent concentration of [total cations*] and [SO 4 2− + NO3 − ] suggests the involvement of H 2 SO 4 and HNO 3 in the dissolution of silicate   Figure S3b in Supporting Information S1). Based on the charge balance analysis of the equivalent ionic concentrations resulting from rock weathering, it is found that H 2 CO 3 and H 2 SO 4 are mostly responsible for the ionic balance which is 46% ± 18% and 45% ± 0.1%, respectively, whereas HNO 3 is responsible for 9% ± 0.8% in our study area.

Chemical Weathering and CO 2 Consumption Rates
The calculated results for chemical weathering and associated CO 2 consumption rates are listed in Table 3 for three different scenarios that is, chemical weathering caused by (a) H 2 CO 3 , H 2 SO 4 , and HNO 3 together as weathering agents, (b) H 2 CO 3 and H 2 SO 4 , and (c) H 2 CO3 only. Results show that in the study area, the rate of carbonate weathering (CWR) is higher than the rate of SWR. Since the calculation of the SWR (Equation 27) depends on the molar concentration of total cations derived from SWR and dissolved silica, irrespective of which weathering agents cause weathering, the calculated SWR rates for the three different scenarios are the same and the average value is (0.95 ± 0.37) × 10 2 tons km −2 yr −1 (n = 33, 1 S.D.). As for carbonate rocks, the average weathering rate is (0.82 ± 0.37) × 10 2 tons km −2 yr −1 (n = 34, 1 S.D.) when only H 2 CO 3 is involved ([CWR] H2CO3 ). Rates of carbonate weathering increase when other acids are involved such as the average of (1.37 ± 0.54) × 10 2 tons km −2 yr −1 (n = 34, 1 S.D.), when carbonic and sulfuric acids are weathering agents and the average of (1.45 ± 0.54) × 10 2 tons km −2 yr −1 (n = 34, 1 S.D.), when carbonic, sulfuric, and nitric acids are involved together. So, the results showed that when H 2 SO 4 is added to H 2 CO 3 as weathering agent, [CWR] H2CO3+H2SO4 increased 1.7 times or 67% compared to [CWR] H2CO3 whereas, when HNO 3 is added to H 2 SO 4 and H 2 CO 3 there is 1.06 times or 5.7% increment for [CWR] H2CO3+H2SO4+HNO3 compared to [CWR] H2CO3+H2SO4 and overall 1.8 times or 77% increment compared to [CWR] H2CO3 . These results imply that the addition of sulfuric and nitric acids enhances carbonate weathering rates and can play important role in accelerating the breakdown of carbonate minerals during chemical weathering (Figure 5a and Table 3a).
The average value of CO 2 consumption rates (ΦCO 2) shows that CO 2 flux is much higher for SWR compared to carbonate weathering ( Figure 5b and Table 3b). The rates of CO 2 consumption are greatly influenced when H 2 SO 4 and HNO 3 are involved in both silicate and carbonate weathering. In the case of only H 2 CO 3 acid-induced SWR the average ΦCO2 sil is (40 ± 17) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) which is changed to (22 ± 11) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) when caused by H 2 CO 3 and H 2 SO 4 to (20 ± 12) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) when H 2 CO 3 , H 2 SO 4 , and HNO 3 are weathering agents. Similarly, the ΦCO2 carb decreases from (6.83 ± 3.1) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) when only H 2 CO 3 is involved, to (4.91 ± 2.7) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) for H 2 CO 3 and H 2 SO 4 induced weathering, to (4.62 ± 2.7) × 10 5 mol km −2 yr −1 (n = 33, 1 S.D.) when H 2 CO 3 , H 2 SO 4 , and HNO 3 all are involved in chemical weathering ( Figure 5b and Thus, the involvement of H 2 SO 4 and HNO 3 along with H 2 CO 3 in chemical weathering increases the CWR but decreases atmospheric CO 2 consumption rates for both silicate and carbonate weathering. Thus, the role of H 2 SO 4 and HNO 3 in chemical weathering should be considered in the local carbon cycle as well as in the global carbon cycle to avoid the overestimation of CO 2 drawdown. Figure 5 shows the seasonal changes in rates of chemical weathering and CO 2 consumption for both carbonate and silicate rocks over the entire ablation season in 2019. The results indicate that the rate of chemical weathering begins to increase in July and reaches its peak in August and then again started to decrease as the melting season progresses (Figure 5a). The trend of weathering rates is the same irrespective of the types of weathering agents involved. Here, we are discussing only the results calculated for all three acid-induced weathering scenarios. During the monsoon period, the average rate of carbonate weathering is (1.76 ± 0.40) tons km −2 yr −1 , while during the pre-monsoon period, it is 1.04 ± 0.52 and 1.22 ± 0.42 tons km −2 yr −1 in the post-monsoon period. Similarly, the SWR rate shows a higher value during the monsoon season, with an average of 1.27 ± 0.35 tons km −2 yr −1 compared to an average of 0.64 ± 0.10 and 0.81 ± 0.26 tons km −2 yr −1 during pre-monsoon and post-monsoon period, respectively. Overall, the rates of carbonate weathering and SWR were approximately 1.5 times and 1.7 times higher during the monsoonal period compare to the non-monsoon periods respectively.

Seasonal Variations in Rates of Chemical Weathering and Associated CO 2 Consumption
The seasonal variation of the CO 2 consumption rate (ΦCO2) follows the same trend as that of the chemical weathering rate (Figure 5b). The highest ΦCO2 are observed during peak monsoon time, with an average value of 7.30 ± 1.93 × 10 5 and 29.34 ± 12.63 × 10 5 mol km −2 yr −1 for carbonate and silicate rock weathering, respectively. During the monsoon period, the (ΦCO2) carb are 3 times and 2.1 times higher compared to pre-monsoon that is, 2.51 ± 0.70 × 10 5 mol km −2 yr −1 and post-monsoon periods, that is, 3.38 ± 2.02 × 10 5 mol km −2 yr −1 , respectively. Similarly, (ΦCO2) sil during the monsoon period increases by a factor of 2.7 and 1.8 respectively, compared to pre-monsoon and post-monsoon periods, with average values of (10.73 ± 4.52) × 10 5 and (15.48 ± 6.97) × 10 5 mol km −2 yr −1 , respectively.

Controlling Factors of the Rates of Chemical Weathering and CO 2 Consumption
Factors that can significantly influence the chemical weathering rate and associated CO 2 consumption rate are lithology, discharge/precipitation, water temperature, and physical weathering rate (PER) (Dupré et al., 2003;Goudie & Viles, 2012;Krishnaswami & Singh, 2005;Wolff-Boenisch et al., 2009). However, the relationship between PER and chemical weathering rate could not be determined due to the lack of data. The seasonal trend of rates of chemical weathering shows that carbonate weathering is higher than SWR by a factor of 1.5 on average, for the case when H 2 CO 3 , H 2 SO 4 , and HNO 3 are involved in weathering. This difference probably due to the fact that the CWR is 12 times higher than that of granites (Meybeck, 1987).
The relationships between chemical weathering rates and associated CO 2 consumption rates with meltwater temperature and discharge are shown in Figure S4 in Supporting Information S1. The relationship between temperature and chemical weathering rates can be described by the Arrhenius-type laws (White et al., 1999), indicating that an exponential function provides a better fit than other equations. Carbonate and SWR rates show a positive trend with water temperature but do not show a good correlation. On the other hand (ΦCO2) carb rate does not show any apparent correlation with seasonal water temperature changes. In contrast, s (ΦCO2) sil rate shows a positive trend with water temperature. However, overall, a low correlation coefficient suggests that water temperature is Figure 5. Comparison of (a) Chemical weathering rates of carbonates and silicates and (b) rates of CO 2 consumption (ΦCO 2 ) for weathering of carbonates and silicates for three different conditions such as weathering induced by (a) carbonic, sulfuric, and nitric acid together as weathering agents, (b) carbonic and sulfuric acids together, and (c) carbonic acid only. Insets show seasonal variation in the rates of (a) chemical weathering rates and (b) CO 2 consumption caused by carbonic, sulfuric, and nitric acids together. Figure 6. Impact of chemical weathering on inorganic CO 2 balance. (a) Short-term (<10 Ky) CO 2 balance (b) medium-term (>10 Ky) CO 2 balance when chemical weathering is caused by (a) carbonic, sulfuric, and nitric acids together as weathering agents and (b) carbonic and sulfuric acid only. (c) Comparison of CO 2 balance for the short-term, medium-term, and long-term (>1 My) when chemical weathering is caused by all three weathering agents.

10.1029/2023GC010919
18 of 21 When the weathering products of H 2 SO 4 and HNO 3 -induced carbonate (Equations 9 and 10 in Table 2b) precipitate in the ocean, 1 mol of Ca 2+ and 1 mol of sedimentary C are removed from the ocean as CaCO 3 and 1 mol of sedimentary C are released as CO 2 into the atmosphere (Calmels et al., 2007) Equation 40 shows that 1 mol of Ca 2+ and SO4 2− is produced from that reaction. Over the timescale of sulfate residence time (>10 7 yr) (Berner et al., 1983;Claypool et al., 1980), the reduction of sulfate associated with oxidation of organic matter counterbalances the previous reaction by releasing 1 mol of sedimentary C.
The existing carbon cycle models of the late 20th century typically assumed that SWR acts as positive feedback by consuming atmospheric CO 2 whereas carbonate weathering is carbon neutral since CO 2 consumed by this weathering gets balanced by the CO 2 released due to secondary precipitation of carbonate by a timescale of 10 ky (Brady, 1991;Brown et al., 1996;Ludwig et al., 1999;Sharp et al., 1995;Tranter et al., 2002;Walker et al., 1981). Therefore, it is considered that atmospheric CO 2 drawdown during SWR induced by H 2 CO 3 led to the Cenozoic cooling (Caves Rugenstein et al., 2019;Raymo & Ruddiman, 1992;Raymo et al., 1988). However, our study suggests that it is important to consider the impact of H 2 SO 4 and HNO 3 in the carbon cycle model to avoid the overestimation of net inorganic CO 2 balance on short-and medium-term time scales. Unlike H 2 CO 3, weathering agents such as H 2 SO 4 and HNO 3 -induced SWR do not cause either drawdown or release of CO 2 (Bufe et al., 2021;Torres et al., 2017), whereas H 2 SO 4 and HNO 3 -induced carbonate weathering could act as a source of atmospheric CO 2 (Calmels et al., 2007;Gandois et al., 2011;W. Liu et al., 2023;Martin, 2017;Perrin et al., 2008;Torres et al., 2016). The release of CO 2 due to H 2 SO 4 and HNO 3 -mediated carbonate weathering can decrease the net CO 2 drawdown, resulting in a reduction of the carbon "sink" in short-and medium-term timescales. Thus, H 2 SO 4 as well as HNO 3 -induced chemical weathering can act as an additional negative feedback mechanism to the "erosion hypothesis" proposed by Raymo and Ruddiman (1992), without adding alkalinity that removes CO 2 from the atmosphere. This study also implies that the drawdown and emission of CO 2 on millennial to multi-million-year timescales depends on the relative changes in the contributions of H 2 CO 3 , H 2 SO 4 , and HNO 3 in both carbonate and SWR. Therefore, the release of CO 2 due to the weathering of carbonates by H 2 SO 4 and HNO 3 acids contradicts the conventional view that carbonate weathering is carbon neutral and does not have climate implications.

Conclusion
The results of the geochemical analysis of meltwater reveal the following comprehensive understanding of the chemical weathering process and its effect on climate, occurring in a small glacierized basin of central Himalaya during a whole ablation season. The meltwater chemistry is dominated by Ca 2+ and Mg 2+ cations, and HCO3 − anion closely followed by SO4 2− . The observed weathering patterns suggest that carbonate weathering is the dominant weathering process and this is most likely due to the limited supply of carbonate rocks and the rapid reaction kinetics of carbonates with strong acids. Moreover, the addition of HNO 3 to H 2 SO 4 and H 2 CO 3 increases the weathering rates of carbonate minerals by 1.06 times compared to the same caused by H 2 CO 3 and H 2 SO 4 together. Consequently, the involvement of HNO 3 decreases atmospheric CO 2 sequestration rates for both carbonate and SWR, similar to the effect of H 2 SO 4 . The rates of CO 2 consumption decrease 1.13 times and 1.06 times due to silicate and carbonate weathering induced by all three acids compared to the same caused by a combination of H 2 CO 3 and H 2 SO 4 . Additionally, the trend of the rates of chemical weathering and associated CO 2 consumption shows notable seasonal variations. Both silicate and carbonate weathering and associated CO 2 consumption rates show significantly higher values during the monsoonal season compared to non-monsoonal