## 3 Results
### Lithological Description  
The sediment cores from LGSP and LCSP are characterised by two main units (Figure 3). The lower section is characterised by a light grey to beige coarser layer with higher MS values in both cores, whereas silty clay sediments compose the upper finer section.  
Laguna Grande de San Pedro (LGSP)  
The basal unit (58-47 cm) is mainly composed of silty sand. The sand fraction \(>\) 63 \(\upmu\)m averaged 14.5 \(\pm\) 3.8% (Table 3). The highest MS values compared to the rest of the sediment core, averaged 299 \(\pm\) 149.9 \(\times\) 10\({}^{-8}\). TOC and TN displayed a gradual increase from the bottom upwards, from 0.5 to 1.7% and 0.05 to 0.17%, respectively. BSi concentrations were low, ranging from 0.35 to 1.19% (0.79 \(\pm\) 0.24%). The C/N ratio varied from 8.7 to 10.3 (9.4 \(\pm\) 0.5). The \(\delta^{13}\)C was stable, ranging between \(-\)25.8% to \(-\)26.2% (\(\pm\)0.3%). Slight variations in \(\delta^{15}\)N values ranged from 3.04 to 5.01% (3.63 \(\pm\) 0.4%) at the bottom with a maximum at 48 cm.  
Figure 2: Chronology of the top centimetres of the Laguna Grande (**a**,**b**,**e**) and Laguna Chica (**c**,**d**,**f**) de San Pedro. The dark line represents the age model, while the grey shades represent the estimated errors, and the vertical and grey lines indicate the coring year.  
Unit 2 (46-0 cm): the grain-size distribution was relatively stable, with a slight variation at the top of the core, with a high amount of silt fraction (\(\sim\)91%). Steady low MS values (85.6 \(\pm\) 19.4 \(\times\) 10\({}^{-8}\)) were observed. Instead, TOC and TN profiles showed a gradual increase upward of this unit. BSi concentrations showed distinguished increases at 29, 12 and 8 cm, while values more than ten in C/N ratios were found from 46 cm to the top of the core. 5\({}^{13}\)C values were stable from 46 to 6 cm, with a trend toward more negative values from 7 cm to the top. 8\({}^{15}\)N values showed marked variations, extending from 3.5 to 6.9% (4.6 \(\pm\) 0.7%), with a significant increase at 24 cm.  
Figure 3: Depth profiles of magnetic susceptibility (SI), organic matter (%), biogenic silica (%), TOC (weight %), C/N ratio atomic, \(\delta^{13}\)C (%) and \(\delta^{15}\)N (%) in sediment core of **(a)** Laguna Grande de San Pedro (LGSP) and **(b)** Laguna Chica de San Pedro (LCSP).  
\begin{table}
\begin{tabular}{c c c c} \hline  & \multicolumn{3}{c}{**Laguna Grande de San Pedro**} \\ \cline{2-4}  & Clay (\%) & Silt (\%) & Sand (\%) \\ \hline UNIT 2 (46–0 cm) & 7.12 \(\pm\) 0.83 & 90.75 \(\pm\) 1.95 & 2.03 \(\pm\) 2.38 \\ UNIT 1 (60–47 cm) & 4.64 \(\pm\) 0.91 & 80.88 \(\pm\) 4.13 & 14.48 \(\pm\) 3.76 \\ \hline  & \multicolumn{3}{c}{**Laguna Chica de San Pedro**} \\ \cline{2-4}  & Clay (\%) & Silt (\%) & Sand (\%) \\ \hline UNIT 2 (93–0 cm) & 7.05 \(\pm\) 2.45 & 90.12 \(\pm\) 4.09 & 2.83 \(\pm\) 2.72 \\ UNIT 1 (120–94 cm) & 4.68 \(\pm\) 1.62 & 87.82 \(\pm\) 2.86 & 7.50 \(\pm\) 2.65 \\ \hline \end{tabular}
\end{table}
Laguna Chica de San Pedro (LCSP)  
Unit 1 (117-94 cm): for LCSP (Figure 3b) showed the highest mean values at the bottom of the core for the mean grain size distribution (15.3 \(\pm\) 3.8%) and the MS profile (\(642\pm 329\times 10^{-8}\)). In contrast, the lowest values were observed for TOC and TN (0.25 \(\pm\) 0.07 and 0.03 \(\pm\) 0.005, respectively). BSi displayed relatively constant values, with an average of 0.5 \(\pm\) 0.23%. The C/N ratio fluctuated from 5.4 to 10.4, while the \(\delta^{13}\)C and \(\delta^{15}\)N showed more negative values at 102 cm.  
Unit 2 (94-0 cm): the grain-size particle displayed variations throughout the core. Steady MS values were observed (85.6 \(\pm\) 19.4 \(\times\) 10\({}^{-8}\)). A notable shift was observed in mean grain size, MS, TOC, TN, BSi, C/N, \(\delta^{13}\)C and \(\delta^{15}\)N between 66 and 58 cm.