Paleoenvironmental reconstruction in La Paz Bay,Gulf of California: Evidence from δ 18 O in Chione californiensis

Abstract

Oceanic characteristics of the Holocene are used to understand climatic patterns and phenomena that affect marine and human communities. Likewise, past marine conditions can be reconstructed from surface sea temperature (SST), using stable oxygen isotopes in bivalve shells. The objective of this study was to calculate Holocene summer SSTs for La Paz Bay, by analyzing δ¹⁸O of ¹⁴C dated bivalve shells (Chione californiensis) from a Holocene camp site located in Cañada de La Enfermería, Baja California Sur, México. Aragonite was extracted from the shells’ umbo, representing the summer growth season during the first year of life. δ¹⁸O value of C. californiensis is −1.9 ± 0.1‰ at present, and varied between −1.3‰ and −2.6‰ during the last 9 ky. In 9469 BP, 8396 BP, and 7708 BP, δ¹⁸O values were similar to those of the present. In 7857 BP, 7805 BP, and 7804 BP, δ¹⁸O was ¹⁸O depleted (0.6–0.9‰), indicating warmer summer SSTs versus the present. In 7070 BP, 6945 BP, and 2087 BP, δ¹⁸O was enriched in ¹⁸O (0.3–0.4‰), suggesting colder SSTs versus the present. This study coincides with other paleotemperature studies for the region and allows us to address the effect of changing SST on this marine resource, its use by human communities of the past, and its effects on human presence in the area with respect to climate variability.

Keywords

climatic variation environmental reconstructions human subsistence Mollusk shells stable oxygen isotopes

Introduction

Early Holocene archeological evidence indicates that the settlement of Baja California was mainly carried out by coastal groups from western Canada and the northwestern United States, as well as groups from the Western Pluvial Lakes tradition, which adapted to coastal life as they arrived in the Cape region around 12,000 BP (Fujita, 2010; Porcasi and Fujita, 2011),

La Paz Bay contains a diversity of archeological sites, suggesting a process of early settlement (Figure 1). These sites present mounds of discarded domestic waste, composed mainly of faunal remains and lithic materials. Their analysis reveals great dependence on marine mollusks, echinoderms, crustaceans, fish, cetaceans, turtles, marine mammals, and the complementary use of terrestrial plant and animal resources (Fujita and Ainis, 2018). Coastal shell sites are valuable reference points of prehistoric times and have been used as environmental monitoring tools (Braje et al., 2009; Leng and Lewis, 2016), providing a wide-spectrum and high-resolution archive of changes in ocean temperature and chemical conditions, under which these mollusk shells were formed (Colonese et al., 2012; Gordillo et al., 2015; Schöne, 2008; Schöne and Gillikin, 2013).

Figure 1.

Location of the archeological site Cañada de La Enfermería, La Paz, B.C.S., Mexico. The segmented line represents the coastline at −16.25 m ca. 8000 BP, relative to the actual coastline.

The bivalve genus Chione is widely represented in natural and archeological sites of the Gulf of California (Goodwin et al., 2001; Meldahl, 1995; Meldahl and Cutler, 1992), Pacific coasts (Laylander and Iversen, 2006; Rick et al., 2004), and other parts of the world (Edie and Surge, 2013; Keyes, 1960). Moreover, Chione californiensis (C. californiensis) is one of the most representative species in archeological sites of La Paz Bay (Ainis et al., 2019; Rosales-López et al., 2003), making it a proxy for paleoceanographic studies, and enabling for a detailed view of the marine environment from which the inhabitants of the region extracted this resource. This bivalve is distributed in the Pacific Ocean from Punta Mugu, California, USA to Panama. It lives mainly in the intertidal zone (up to a depth of 69 m) and can frequently be found buried a few centimeters below the sediment surface (Prado-Ancona, 1998). It can live up to 18 years and decreases shell growth after four years. Its distribution and abundance are related to temperature, salinity, dissolved oxygen, as well as the amount of organic matter and sediment granulometry (García-Dominguez et al., 1994).

Sea surface temperature (SST) largely determines the distribution and availability of this species, with an optimal threshold between 24°C and 27°C for the genus Chione (Celis-Hernández, 2011). The reproduction of C. californiensis in La Paz Bay lasts 8 months, interrupted during winter between 18°C and 23°C (García-Dominguez, 1991). Additionally, the species presents an optimum growth period in the summer season (García-Dominguez, 1991), during which there is a deep nutricline and a stratified water column (Obeso-Nieblas et al., 2014).

Most organisms that precipitate calcium carbonate do so under conditions of isotopic equilibrium with seawater. This mechanism, mainly dependent on temperature, determines the proportion of oxygen isotopes in biogenic carbonate at a rate of 0.24‰ per °C (Epstein et al., 1953). A study on mollusk δ¹⁸O of Mid-Holocene shell middens in Santa Rosa Island, California found a significant SST change of 2°C between 6000 BP and 4300 BP (Rick et al., 2006). Similarly, for the Colorado River Delta, Gulf of California, late-Holocene exploitation of coastal resources by humans and environmental conditions were inferred through δ¹⁸O analysis of shell middens. Values ranged from −3.05‰ to 0.7‰, with an average of −0.87‰ for 2500 BP (Celis-Hernández, 2011). Additionally for the same region, the species Chione cortezi (currently accepted name Chionista fluctifraga) was cross calibrated to infer SST through δ¹⁸O analysis, establishing an annual seasonal difference of 3.38‰ (15.9°C) (Schöne et al., 2003).

Studies on SST variability and its implications on past marine ecosystems are limited for the La Paz Bay. However, coccolithophore and silicoflagellate records suggest water column variability due to nutricline oscillation between 9000 BP and 6000 BP (Staines-Urías et al., 2015), warm SSTs due to the incursion of tropical waters during 5528 BP, 4500 BP, 3750 BP and in the recent past, as well as cold SSTs between 3495 BP and 2250 BP (Álvarez et al., 2012).

The present study aims to reconstruct the paleo-environment of La Paz Bay (Gulf of California) and analyze subsistence strategies of human communities that inhabited the region through stable oxygen isotope analysis of C. californiensis shells collected from a Holocene camp site in a subtropical bay of the southern Gulf of California.

Environmental and archeological setting

Study area

The Gulf of California is a unique, narrow, and semi-closed marginal sea. Moreover, it is the only evaporative basin of the Pacific Ocean, where evaporation process historically dominate regional oceanographic dynamics (Beron-Vera and Ripa, 2002). The La Paz Bay is an important body of water within the Gulf. It is influenced by southern Gulf of California mesoscale processes, which largely determine its hydrographic conditions (Obeso-Nieblas et al., 2008). The SST of La Paz Bay varies seasonally with a maximum of 28°C during summer and autumn seasons, later decreasing to 19°C at the end of winter (Obeso-Nieblas et al., 2014). Specifically, in the island complex of Espíritu Santo, summer in situ SST reached 27.5°C ± 1°C and decreased below 22°C during winter (Aguiñiga et al., 2010).

Geological and archeological setting

La Cañada de La Enfermería is located in the southern region of La Paz Bay, Gulf of California (24°13′14.00″N; 110°16′56.00″W) (Figure 1). It lies on a canyon terrace 3 km from the coast and 70 m above sea level, covering an area of approximately 9000 m², separated by a seasonal stream that runs from north to south. The area is situated on the margin of a structural elevation to the east of the La Paz Valley. It is composed of lithic tuff strata belonging to the Upper Miocene Comondú Formation and is adjacent to a Mesozoic Granitic batholith. It’s topographic elevation drops sharply toward the La Paz Bay with canyons up to 100 m deep, cutting the Comondú Formation from east to west, and generating stream beds that drain significant volumes of water into the bay during the rainy seasons (Padilla-Arredondo et al., 1985). Here several seasonal streams and natural dams were identified, which periodically store abundant fresh water (Figure 2). In addition, the surrounding hills provide various types of lithic raw materials for tool making, and multiple rock shelters that offer protection. Archeological excavations produced a large number of fauna and lithic artifacts dated between 10000 BP and 1800 BP, including projectile points, knives, scrapers, perforators, metate hands, beads, shell hooks, and coral polishers. Its stratigraphy suggests numerous occupational episodes that span much of the Holocene, indicating that it may have been a meeting place for various groups in the region (Figure 3) (Fujita et al., 2018).

Figure 2.

General view of Cañada de La Enfermería (a) and excavation units S1 and S2. Natural freshwater damns (b) (modified from Fujita et al., 2018).

Figure 3.

Bivalve and lithic artifact remains at excavation unit 1 (a), and Stratigraphic layers (b) at excavation unit 2, Cañada de La Enfermería, La Paz bay.

Materials and methods

Collection and dating of bivalves

The collection of shells at Cañada de La Enfermería was carried out in 2015 and 2016 as part of the INAH archeological project Registration and Excavation of the archeological sites of the municipality of La Paz, B.C.S. The non-disturbed stratigraphic layers (with no apparent sign of mixing) of two excavation units (Figures 2a and 3) were dated with one mollusk ¹⁴C analysis per layer at the National Institute of Anthropology and DirectAMS, yielding estimated dates between 10000 BP and 1500 BP (±29 to 179 years). Due to laboratory protocols, the dated bivalve shells were utilized in their entirety (Fujita et al., 2018). Additionally, representative bivalve specimens from each stratigraphic layer were taxonomically identified to species (Coan and Valentich-Scott, 2012).

Bivalve shell isotope analysis

Given the continuous presence of C. californiensis in the stratigraphic layers and its representativeness at a regional level, the species was selected as a proxy for this study.

Three well preserved specimens of C. californiensis with similar sizes were selected from each dated stratigraphic layer (9469 BP, 8396 BP, 7857 BP, 7805 BP, 7804 BP, 7708 BP, 7070 BP, 6945 BP, 2087 BP). Additionally, three live specimens were collected in August 2020 in the La Paz Bay, as reference to present day conditions, totaling 28 individuals for 10 dates (nine stratigraphic layers and the present).

The genus Chione in the Gulf of California is represented by species analogous to C. californiensis (i.e. C. fluctifraga and C. Cortezi) with shells composed exclusively of calcium carbonate in the form of aragonite (Goodwin et al., 2001; Schöne et al., 2006). In order to obtain aragonite for oxygen isotope analysis, the surface layer of each shell was cleaned to remove organic residues (Culleton et al., 2006 C. californiensis). The shells were then placed in a 1.5% sodium hypochlorite solution for 24 h and rinsed with distilled water in an ultrasonic bath, removing residual impurities. Finally, aragonite was obtained using a microdrill, extracting approximately 1 mg of calcium carbonate powder from the inner face of each shell, in close proximity to the umbo, guaranteeing similar age intervals. This extraction point corresponds to the optimal growth season (summer) of (García-Dominguez, 1991) during the first year of life (Robbins, 2006) (Figure 4).

Figure 4.

Chione californiensis microsampling of shells from the past (a) and present (b). The calcium carbonate extraction point (using a 5 mm drill bit) can be seen adjacent to each shell’s umbo, corresponding to the species optimal growth season (summer) during its first year of life.

The aragonite microsamples were processed and analyzed at the University of Wyoming’s Stable Isotope Facility. Samples were placed in exentainer tubes, purged with ultrapure He to evacuate all air, and digested with 100% orthophosphoric acid at 25°C for 8 h. The CO₂ generated was analyzed in a Thermo Gas Bench-II, and subsequently the oxygens’ isotopic ratio was determined using a Delta V plus mass spectrometer (McCrea, 1950). Results were expressed in δ notation (‰ vs VPDB). The analytical precision of three standards used were 0.19-18UWY, 0.09-6UWY, and 0.07-17UWY‰, respectively.

Paleotemperatures

For paleotemperature calculations Grossman and Ku’s (1986) empirical relationship, modified by Schone et al. (2001) for Chione cortezi was used:

T = 20.6 - 4.34 (δ^{18} O - (δ^{18} Osw - 0.2))

where T is expressed in degrees Celsius, δ¹⁸O (‰ vs VPDB) is the isotopic value of aragonite and δ¹⁸Osw (‰ vs SMOW) is the average change in δ¹⁸O for the Pacific Ocean with a value between −0.01 and 0‰ (LeGrande and Schmidt, 2009).

Results

Through the use of the paleotemperature equation, modified by Schone et al. (2001), the isotopic equilibrium of aragonite was calculated considering an average SST of 28°C (Aguiñiga et al., 2010; Obeso-Nieblas et al., 2008) and a seawater isotopic value of 0‰ (LeGrande and Schmidt, 2009). The δ¹⁸O value of the aragonite at isotopic equilibrium was −1.9‰, very similar to measured value of the C. californiensis shells of the present (−1.9 ± 0.1‰). Therefore, C. californiensis δ¹⁸O is in isotopic equilibrium with its environment and can be used as a paleotemperature proxy. Similarly, Schöne et al. (2006) found that Chione fluctifraga, an analog species from the northern Gulf of California, is also in isotopic equilibrium with its environment.

Chione californiensis δ¹⁸O averages are presented for one modern date (La Paz Bay specimens collected in 2020) and nine archeological intervals (dated stratigraphic layers) of Cañada de La Enfermería (Table 1). Modern δ¹⁸O values averaged −1.9 ± 0.1‰, while past average values ranged between −1.6 ± 0.3‰ and −2.2 ± 0.4‰ (Table 1, Figure 5).

Table 1.

Chione californiensis sample ID, graph reference, average δ¹⁸O values and standard deviation for specimens of La Cañada de La Enfermería, La Paz Bay. Sea surface temperature (SST in °C) estimated using Grossman and Ku’s (1986) paleotemperature equation. Age range (Fujita et al., 2018) and average (years BP, 1-SIGMA).

Samples	Reference	δ¹⁸O (‰ vs. VPDB)		SST		Age average	Age range
Samples	Reference	Average	SD	Average	SD	BP	BP
BLP	10	−1.9	±0.1	28.7	0.6	0	0
En/U2/III-b	9	−1.6	±0.3	27.2	1.4	2087	2206–1967
En/U2/III-f	8	−1.7	±0.1	28.2	0.9	6945	7072–6817
En/U2/III-d	7	−1.7	±0.2	28.1	0.4	7070	7200–6940
En/U2/IV-c	6	−1.9	±0.4	29.1	1.6	7708	7809–7606
En/U1/II-b	5	−2.0	±0.5	29.5	2.2	7804	7855–7752
En/U2/IV-b	4	−2.1	±0.2	29.7	1.0	7805	7915–7695
En/U1/II-a	3	−2.2	±0.4	30.1	1.8	7857	7908–7806
En/U1/III-e	2	−1.9	±0.1	28.8	0.4	8396	8438–8353
En/U2/VI-d	1	−1.9	±0.2	29.1	0.6	9469	9505–9433

Figure 5.

δ¹⁸O mean values and standard deviations versus age of C. californiensis specimens from the archeological excavation site Cañada de La Enfermería, Bahía de La Paz, México. Numbered circles correspond to sample references (Table 1). The dotted box represents δ¹⁸O variation in the present.

Specifically, average δ¹⁸O values for 9469 BP and 8396 BP were very similar to present values (both −1.9‰). During the period between 7857 BP and 7804 BP, average δ¹⁸O values exhibited ¹⁸O depletion of up to 0.3‰ with respect to the modern value (−1.9‰), progressively increasing from −2.2‰ to −2.0‰. δ¹⁸O values for the year 7708 BP further increased toward present values (−1.9‰). This tendency continued during 7070 BP (−1.7 ± 0.2‰) and 6945 BP (−1.7 ± 0.1‰). In 2087 BP, δ¹⁸O values reached a maximum average (for the data series) of −1.6 ± 0.3‰. Finally, between 2087 BP and the present, δ¹⁸O values decreased by 0.3‰.

Inferred summer SSTs for the Cañada de La Enfermería archeological record varied from 27.2°C ± 1.4°C to 30.1°C ± 1.8°C, presenting a range of 2.9°C for the last 9469 years (Table 1, Figure 6). The average summer SSTs in 9469 BP (29.1°C ± 0.6°C) and 8396 BP (28.8°C ± 0.4°C) were very similar to the inferred SST of the present (28.7°C ± 0.6 °C). SST between 8396 BP (28.8 °C ± 0.4°C) and 7857 BP (30.1°C ± 1.8°C) increased by 1.3°C then quickly (within 149 years) decreased to 29.1 ± 1.6°C by 7708 BP, resulting in a SST very similar to that of the present (29.1°C). This decreasing tendency continued from 7070 BP (28.1°C ± 0.4°C) and reaching 28.2°C ± 0.9°C by 6945 BP (0.5°C below the present value) before the archeological record subsides marking the beginning of a 4858-year long hiatus. Subsequently, the first late-Holocene archeological record indicates that in 2087 BP the SST reached a minimum (for the entire data series) of 27.2 °C ± 1.4°C, increasing thereafter by 1.5°C until reaching its present value.

Figure 6.

Inferred summer SST mean values and standard deviations versus age of C. californiensis specimens from the archeological excavation site Cañada de La Enfermería, Bahía de La Paz, México. Numbered circles correspond to sample references (Table 1). The dotted box represents the SST variation in the present.

Discussion

The global Holocene climate has been highly variable, with specific regions responding differently or asynchronously to rapid climate change events that is, Optimal Climate Medieval or Little Ice Age (Boretto et al., 2013; Wanner et al., 2008). However, Holocene climate changes have been strong enough to generate significant effects on ecosystems and human populations (Mayewski et al., 2004). The stable isotope data from Cañada de La Enfermería provides important insight on oceanographic conditions throughout the Holocene. The results obtained here indicate SST change throughout this epoch, and possible effects on ancient human populations of La Paz Bay.

Surface sea temperatura (SST): La Paz Bay

Precipitation of aragonite and/or calcite in various marine organisms including bivalves is dependent on temperature and seawater isotopic composition (Epstein et al., 1953). Therefore, the use of bivalves as SST proxies requires their isotopic equilibrium with the environment throughout their life span (Schone et al., 2001). Using SST and salinity records of La Paz Bay (Aguiñiga et al., 2010; Obeso-Nieblas et al., 2008), as well as the modified paleotemperature equation by Schone et al. (2001). Aragonite δ¹⁸O values was calculated in equilibrium with seawater. The δ¹⁸O value in equilibrium obtained was −1.8 ± 0.2‰, very similar to the C. californiensis δ¹⁸O value of −1.9 ± 0.1‰ (n = 3) for the present. This suggests that δ¹⁸O values of C. californiensis are adequate for inferring past SSTs of La Paz Bay, as has been suggested for other bivalves in the Gulf of California (Celis-Hernández, 2011; Schöne et al., 2003) and California (Rick et al., 2006).

The C. californiensis δ¹⁸O values of the present indicate a mean summer SST of 28.6°C ± 0.6°C, which is closely similar to the mean in situ SST of the bay and the island complex of Espíritu Santo (Aguiñiga et al., 2010), validating C. californiensis as an adequate SST proxy of La Paz Bay. Additionally, the δ¹⁸O values of the C. californiensis specimens from the past can also be considered SST indicators.

SST of 9469 BP and 8396 BP

The calculated summer SST of 9469 BP (29.1°C; −1.9 ± 0.2‰) and 8396 BP (28.8°C; −1.9 ± 0.1‰) were very similar to the summer SST of the present (28.7°C; −1.9 ± 0.1‰). During the summer season, oceanographic conditions in the bay are characterized by a stable and stratified water column dominated by the tropical surface water mass (Obeso-Nieblas et al., 2008). Although these oceanographic conditions limit marine productivity due to a deep nutricline, the SST recorded for this time interval is optimal for C. californiensis growth (García-Dominguez, 1991). Our results suggest that the summer seasons of 9469 BP and 8396 BP presented similar oceanographic conditions. Paleoceanographic records for these periods suggest the presence of warm tropical waters with SSTs > 25°C in the Gulf of California (Barron et al., 2005; McClymont et al., 2012), as well as low primary productivity and reduced upwelling in the southwestern margin of the Baja California peninsula. Moreover, the periods of 9469 BP and 8396 BP were characterized by climatic and oceanographic conditions very similar to those during the El Niño event in the Soledad basin (Marchitto et al., 2010), confirming the inferred conditions of low productivity and warm temperatures for the Pacific Northeast by Barron et al. (2012). Similarly, during this period in La Paz Bay, the abundance of coccolithophore species in deep water cores suggests a stable and deep nutricline with moderate productivity (Staines-Urías et al., 2015).

SST between 7857 BP and 7070 BP

According to our results, the period between 7857 BP (30.1°C; −2.2 ± 0.4‰) and 7070 BP (28.1°C; −1.7 ± 0.2‰), corresponding to the Mid-Holocene Climatic Optimum, presented a local progressive decrease of 2°C in summer SSTs. The change in surface water column conditions may be associated to the incursion and dominance of cooler Gulf of California waters (Monreal-Gomez et al., 2001) versus warmer equatorial surface waters (Obeso-Nieblas et al., 2008), a process which is dominant during the summer season when surface water exchange between the gulf and the bay generally increases (Guevara-Guillén, 2011). Moreover, during this period radiolarian associations in the bay were characterized by Gulf of California species, also suggesting cold and slightly more saline waters (Pérez-Cruz and Urrutia-Fucugauchi, 2009). Similarly, reduced El Niño events were also inferred by the abundance of coccolithophores and silicoflagellates in the bay (Álvarez et al., 2012; Staines-Urías et al., 2015).

In a regional context, during this period oceanographic conditions for the Gulf of California presented great variability within the water column, inferred from the association of diatoms, silicoflagellates and coccolithophores, as well as geochemical variables that is, organic carbon and biogenic opal versus calcium carbonate. Specifically, biogenic opal content exhibited an increase from 22% to 27% in the period between 7857 BP (30.1°C; −2.2 ± 0.4‰) and 6945 BP (28.2°C; −1.7 ± 0.1‰)(Álvarez et al., 2012; Arellano-Torres et al., 2020; Barron et al., 2005; Pérez-Cruz and Urrutia-Fucugauchi, 2009), suggesting a shallowing thermocline, coinciding with an increased presence of the diatom R. tesselata and the silicoflagellate D. stapedii, both indicators of a colder and slightly more saline water column (Barron et al., 2005; Schrader et al., 1986). Additionally, La Niña-like oceanographic conditions and decreased SSTs were recorded for the Gulf of California (Barron et al., 2005), the eastern margin of the Baja California peninsula (Arellano-Torres et al., 2020; Marchitto et al., 2010), and the present study.

SST of 2087 BP

The calculated summer SST of La Paz Bay for 2087 BP (27.2°C; −1.6 ± 0.3‰) was the coldest for the study with respect to the present SST (28.7°C; −1.9 ± 0.1‰). In the bay, decreases in SST have been associated with the upwelling of cold subsurface waters. Additionally, cold thermal fronts of up to 2°C have been recorded inside the bay during the summer season (Coria-Monter et al., 2018). Moreover, in La Paz Bay, O. pulchra and other cold water species presented maximum relative contributions between 2800 BP and 1800 BP (Álvarez et al., 2012), indicating important mixing processes which decrease SST (Barron et al., 2005; Ricaurte-Villota et al., 2013). In general, the late-Holocene has been considered a period of intense El Niño activity (Moy et al., 2002), occasionally interrupted by intense La Niña events (Herguera et al., 2003), and widely documented throughout the northeastern Pacific basin (Barron and Anderson, 2011). During this period the silicoflagellate O. pulchra exhibited a relative abundance >60% for the Gulf of California, indicating a shallow thermocline with high primary productivity.

Human presence

The reconstruction of ancient human societies of the Baja California Peninsula is not an easy task. However, the evidence unearthed by archeologists indicates that human populations in Cañada de La Enfermería depended almost exclusively on the availability of marine resources and fresh water (Fujita et al., 2018). These resources justified frequent travel toward the coast by women, children, and the elderly, generally responsible for the collection of mollusks in ancient native cultures (Palacios-Peñaranda, 2017). The relative and uniform temporal distribution of the stratigraphic layers of Cañada de La Enfermería suggest numerous episodes of occupation throughout most of the past 10,000 years (Fujita et al., 2018). This camp site also followed a chronological occupation pattern similar to that of most mid-Holocene middens of the bay, exhibiting an occupational pause between circa 6585 BP and 2220 BP (Fujita, 2010; Fujita et al., 2018). The absence of archeological records during this period suggests a change in environmental and oceanographic conditions, and/or in the dietary strategies of natives, which led to the abandonment of the area, most likely in search of alternative food sources (Michelot, 2015).

This transition window between the middle and late-Holocene has been recognized as a period of extreme climate change, which includes the events 5200 BP (Magny and Haas, 2004) and 4200 BP (Kathayat et al., 2017), characterized by global cooling and drought, which had drastic global effects on human civilizations (Booth et al., 2005; Cullen et al., 2000; Kathayat et al., 2017, 2018; Liu and Feng, 2012; Magny and Haas, 2004; Roland et al., 2014; Scroxton et al., 2020).

Archeological and paleoenvironmental records of the California Channel Islands for the period between 7500 BP and 3800 BP suggest severe climatic change and effects on its inhabitants, caused by general warm and dry conditions accompanied by low marine productivity, with a period of cold temperatures and severe aridity between 6300 BP and 4800 BP. The impact of this fluctuation on human communities varied according to island’s size, fresh water availability, local productivity with respect to population size, and degree of isolation (Kennett et al., 2007), generating changes in feeding strategies and in some cases the abandonment of entire villages (Glassow et al., 1994; Rick et al., 2006).

Similarly, the Gulf climate was generally warmer and more humid during this period, with decreased marine primary productivity for the southern Gulf of California (Douglas et al., 2001). Moreover, sedimentary records for the Guaymas Basin indicate seasonal tropical water incursions, suggesting a significant SST increase during 5400 BP and 5600 BP (Barron et al., 2005; Keigwin, 2002). Jointly, these changes could explain why humans abandoned Cañada de La Enfermería during much of the Middle Holocene, to then repopulate the area after 2220 BP, coinciding with a change toward colder and drier climatic conditions, and an increase in marine primary productivity as the spring monsoon winds intensified (Douglas et al., 2001).

Palaeoenvironmental evolution

The results of this study indicate that the summer SST of La Paz Bay has varied significantly throughout the Holocene. Early Holocene (9469 BP and 8396 BP) summer SSTs (29.1°C; −1.9 ± 0.2‰ and 28.8°C; −1.9 ± 0.1‰, respectively) were similar to modern summer SST (28.7°C; −1.9 ± 0.1‰), during which oceanographic characteristics were analogous to present conditions, coinciding with the studies by Barron et al. (2005) and McClymont et al. (2012) for the Gulf of California. Subsequently, our results suggest that summer SSTs quickly increased by 7857 BP (30.1°C; −2.2 ± 0.4‰), then slowly decreased until 7070 BP (28.1°C; −1.7 ± 0.2), corresponding to the Mid-Holocene Climatic Optimum, and coinciding with incursions of cold water from the Gulf of California (Pérez-Cruz and Urrutia-Fucugauchi, 2009). For the next 5000 years, evidence of human presence in the bay is scarce, suggesting extreme climatic change that drove human populations to more habitable areas. By 2087 BP (27.2°C; −1.6 ± 0.3‰), humans had once again established themselves in the bay as summer SSTs declined, and upwellings of cold and productive subsurface waters predominated (Álvarez et al., 2012).

Conclusions

The δ¹⁸O values obtained indicate a transition to warmer summer SSTs between 8400 BP and 7800 BP, and a slight change toward colder summer SSTs around 6900 BP. Additionally, in 2087 BP δ¹⁸O values were the most enriched, suggesting colder summer SSTs.

Chione californiensis calculated summer SSTs of the present were similar to in situ summer SSTs, confirming that the calculated paleotemperatures also correspond to summer seasons. Considering the results obtained, C. californiensis is an adequate proxy to reconstruct the paleo-environment of the bay of La Paz.

The human occupational pause evidenced in La Cañada de La Enfermería between 6585 BP and 2220 BP coincides with a period of extreme global climate change, which for the southern Gulf of California exhibited warmer and more humid conditions as well as decreased marine primary productivity.

Footnotes

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Financial support for this study was provided by the proyects SIP2020-0708 and SIP2021-0421 of the Instituto Politécnico Nacional (IPN), as well as the “Beca de estímulo Institucional de Formación de Investigadores BEIFI.” The bivalve samples were provided from the Projects “Poblamiento de América visto desde la isla Espíritu Santo, B.C.S.” and “Registro y Excavación de sitios arqueológicos del Municipio de La Paz, B.C.S.” by the Instituto Nacional de Antropología e Historia (INAH). Fernando Arenas González is supported by Master’s scholarship funded by Consejo Nacional de Ciencia y Tecnología (CONACYT), México. Special thanks to Dr. René Vellanoweth of California State University, Los Angeles for partly financing ¹⁴C dating, and Karim Bulhusen Muñoz for the constant feedback and archeological expertise.

ORCID iD

Fernando Arenas

References

Aguiñiga

Sanchez

Silverberg

(2010) Temporal variations of C, N, δ13C, and δ15N in organic matter collected by a sediment trap at Cuenca Alfonso, Bahía de La Paz, SW Gulf of California. Continental Shelf Research 30(15): 1692–1700.

Ainis

Fujita

Vellanoweth

(2019) The antiquity of pearling in the Americas: Pearl modification beginning at least 8,500 years ago in Baja California Sur, México. Latin American Antiquity 30: 637–643.

Álvarez

Pérez-Cruz

Hernández-Contreras

(2012) Coccolithophore and silicoflagellate records in middle-late-holocene sediments from La Paz basin (Gulf of California): Paleoclimatic implications. Stratigraphy 9(2): 169–181.

Arellano-Torres

Mora-Rivera

Vázquez-Romero

, et al. (2020) Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka. Journal of Quaternary Science 35(3): 479–491.

Barron

Anderson

(2011) Enhanced late Holocene ENSO/PDO expression along the margins of the eastern North Pacific. Quaternary International 235: 3–12.

Barron

Bukry

Dean

(2005) Paleoceanographic history of the Guaymas Basin, Gulf of California, during the past 15,000 years based on diatoms, silicoflagellates, and biogenic sediments. Marine Micropaleontology 56(3–4): 81–102.

Barron

Metcalfe

Addison

(2012) Response of the North American monsoon to regional changes in ocean surface temperature. Paleoceanography 27(3): PA002235.

Beron-Vera

Ripa

(2002) Seasonal salinity balance in the Gulf of California. Journal of Geophysical Research 107(C8): 1–15.

Booth

Jackson

Forman

, et al. (2005) A severe centennial-scale drought in midcontinental North America 4200 years ago and apparent global linkages. The Holocene 15(3): 321–328.

10.

Boretto

Gordillo

Cioccale

, et al. (2013) Multi-proxy evidence of late quaternary environmental changes in the coastal area of Puerto Lobos (northern Patagonia, Argentina). Quaternary International 305: 188–205.

11.

Braje

Erlandson

Rick

, et al. (2009) Fishing from past to present: Continuity and resilience of red abalone fisheries on the Channel Islands, California. Ecological Applications 19(4): 906–919.

12.

Celis-Hernández

(2011) Explotación de recursos costeros y condiciones ambientales en el delta del río Colorado durante la prehistoria. Baja California: Universidad Autónoma de.

13.

Coan

Valentich-Scott

(2012) Bivalve Seashells of Tropical West America. Marine Bivalve Mollusks from Baja California to Peru. Santa Barbara Museum of Natural History, Monographs number 6, studies in biodiversity number 4.

14.

Colonese

Verdún-Castelló

Álvarez

, et al. (2012) Oxygen isotopic composition of limpet shells from the Beagle Channel: Implications for seasonal studies in shell middens of Tierra del Fuego. Journal of Archaeological Science 39(6): 1738–1748.

15.

Coria-Monter

Monreal-Gómez

León

DASD

, et al. (2018) Impact of the “godzilla El Niño” event of 2015–2016 on sea-surface temperature and chlorophyll-a in the southern Gulf of California, Mexico, as evidenced by satellite and in situ data. Pacific Science 72(4): 411–422.

16.

Cullen

DeMenocal

Hemming

, et al. (2000) Climate change and the collapse of the Akkadian empire: Evidence from the deep sea. Geology 28(4): 379–382.

17.

Culleton

Kennett

Ingram

, et al. (2006) Intrashell radiocarbon variability in marine mollusks. Radiocarbon 48(3): 387–400.

18.

Douglas

Gorsline

Grippo

, et al. (2001) Holocene ocean – Climate variations in Alfonso Basin, Gulf of California, Mexico. In: Proceedings of the 18th PACLIM workshop, Asilomar, Pacific Grove, CA, January 2001, pp.7–20.

19.

Edie

Surge

(2013) Deciphering annual growth features in Chione elevata shells using isotope sclerochronology. Palaios 28(2): 93–98.

20.

Epstein

Buchsbaum

Lowenstam

, et al. (1953) Revised carbonate-water isotopic temperature scale. Geological Society of America Bulletin 64(11): 1315–1326.

21.

Fujita

(2010) Prehistoric Occupation of Espíritu Santo Island, Baja California Sur, Mexico. Journal of California and Great Basin Anthropology 30(1): 17–33.

22.

Fujita

Ainis

(2018) Traditions of early human groups in Baja California and possible routes for the peopling of the Peninsula. Western North American Naturalist 78(3): 285–301.

23.

Fujita

Hernández

Bulhusen

, et al. (2018) Trans-Holocene occupations at Cañada de la Enfermería Sureste #3 (Site A119), Baja California Sur, México. Proceedings of the Society for California Archaeology 32: 59–77.

24.

García-Dominguez

(1991) Distribucion, abundancia, reproduccion y fauna asociada a la almeja roñosa, Chione californiensis. Maestría en Ciencias Marinas Thesis, Centro Interdisciplinario de Ciencias Marinas, IPN.

25.

García-Dominguez

Federico Arvizu Martínez

Rodríguez Astudillo

, et al. (1994) Distribución y abundancia de Chione californiensis (Pelecypoda: Veneridae) en la Ensenada de La Paz, Baja California Sur, México. Revista de Biologia Tropical 42(3): 531–536.

26.

Glassow

Kennett

, et al. (1994) Confirmation of Middle Holocene Ocean Cooling Inferred From Stable Isotopic Analysis of Prehistoric Shells From Santa Cruz Island, California. Santa Barbara, CA: Santa Barbara Museum of Natural History.

27.

Goodwin

Flessa

Schone

, et al. (2001) Cross-calibration of daily growth increments, stable isotope variation, and temperature in the Gulf of California Bivalve Mollusk Chione cortezi: Implications for paleoenvironmental analysis. Palaios 16(4): 387–398.

28.

Gordillo

Brey

Beyer

, et al. (2015) Climatic and environmental changes during the middle to late Holocene in southern South America: A sclerochronological approach using the bivalve Retrotapes exalbidus (Dillwyn) from the beagle channel. Quaternary International 377: 83–90.

29.

Grossman

(1986) Oxygen and carbon isotope fractionation in biogenic aragonite: Temperature effects. Chemical Geology: Isotope Geoscience Section 59: 59–74.

30.

Guevara-Guillén

(2011) Hidrografía en Bahía de La Paz y zona oceánica adyacente (2009). Maestría en Manejo de Recursos Marinos Thesis, Instituto Politécnico Nacional.

31.

Herguera

Franco

Molina-Cruz

(2003) Decadal surface ocean variability in the lower Gulf of California: Records for the past 300 years. Geofisica Internacional 42(3): 397–406.

32.

Kathayat

Cheng

Sinha

, et al. (2017) The Indian monsoon variability and civilization changes in the Indian subcontinent. Science Advances 3(12): e1701296.

33.

Kathayat

Cheng

Sinha

, et al. (2018) Evaluating the timing and structure of the 4.2 ka event in the Indian summer monsoon domain from an annually resolved speleothem record from northeast India. Climate of the Past 14(12): 1869–1879.

34.

Keigwin

(2002) Late pleistocene-Holocene paleoceanography and ventilation of the Gulf of California. Journal of Oceanography 58(2): 421–432.

35.

Kennett

Erlandson

, et al. (2007) Human responses to middle Holocene climate change on California’s Channel Islands. Quaternary Science Reviews 26(3–4): 351–367.

36.

Keyes

(1960) The cultural succession and ethnographic features of D’Urville Island. Journal of the Polynesian Society 69(3): 239–265.

37.

Laylander

Iversen

(2006) Genera and prehistoric change on the San Diego County coast. Pacific Coast Archaeological Society Quarterly 39(4): 39–48.

38.

LeGrande

Schmidt

(2009) Sources of Holocene variability of oxygen isotopes in paleoclimate archives. Climate of the Past 5(3): 441–455.

39.

Leng

Lewis

(2016) Oxygen isotopes in molluscan shell: Applications in environmental archaeology. Environmental Archaeology 21(3): 295–306.

40.

Liu

Feng

(2012) A dramatic climatic transition at ~4000 cal. yr BP and its cultural responses in Chinese cultural domains. The Holocene 22(10): 1181–1197.

41.

McClymont

Ganeshram

Pichevin

, et al. (2012) Sea-surface temperature records of termination 1 in the Gulf of California: Challenges for seasonal and interannual analogues of tropical Pacific climate change. Paleoceanography 27(2): 1–15.

42.

McCrea

(1950) On the isotopic chemistry of carbonates and a paleotemperature scale. The Journal of Chemical Physics 18(6): 849–857.

43.

Magny

Haas

(2004) A major widespread climatic change around 5300 cal. yr BP at the time of the Alpine Iceman. Journal of Quaternary Science 19(5): 423–430.

44.

Marchitto

Muscheler

Ortiz

, et al. (2010) Dynamical response of the tropical pacific ocean to solar forcing during the early holocene. Science 330(6009): 1378–1381.

45.

Mayewski

Rohling

Curt Stager

, et al. (2004) Holocene climate variability. Quaternary Research 62(3): 243–255.

46.

Meldahl

(1995) Pleistocene shoreline ridges from tide-dominated and wave-dominated coasts: Northern Gulf of California and western Baja California, Mexico. Marine Geology 123(1–2): 61–72.

47.

Meldahl

Cutler

(1992) Neotectonics and taphonomy: Pleistocene molluscan shell accumulations in the Northern Gulf of California. Palaios 7(2): 187–197.

48.

Michelot

J-L

(2015) Evidence of a prolonged drought ca. 4200 yr BP correlated with prehistoric settlement abandonment from the Gueldaman GLD1 cave, N-Algeria. Climate of the Past Discussions 11(4): 2729.

49.

Monreal-Gómez

Molina-Cruz

Salas-deLeón

(2001) Water masses and cyclonic circulation in Bay of La Paz, Gulf of California, during June 1998. Journal of Marine Systems 30(3–4): 305–315.

50.

Moy

Seltzer

Rodbell

, et al. (2002) Variability of El Niño/Southern oscillation activity at millennial timescales during the Holocene epoch. Nature 420(6912): 162–165.

51.

Obeso-Nieblas

Gaviño-Rodríguez

Obeso-Huerta

, et al. (2014) Variabilidad espacial termohalina, Masas de agua y circulación geostrófica en bahía de la paz, Golfo de california. Revista de Biologia Marina y Oceanografia 49(3): 413–426.

52.

Obeso-Nieblas

Shirasago-Germán

Gaviño-Rodríguez

, et al. (2008) Variabilidad hidrográfica en Bahía de La Paz, Golfo de California, México (1995-2005). Revista de Biologia Marina y Oceanografia 43(3): 559–567.

53.

Padilla-Arredondo

Díaz Rivera

Avilés

(1985) Transgresión Holocénica en la Laguna Costera Enfermería de la Bahía de La Paz, B. C. S., México. Anales del instituto de ciencias del mar y limnología 1983: 1–13.

54.

Palacios-Peñaranda

(2017) Evaluación del almacenamiento de Carbono como servicio ecosistémico en bosques de manglar de la Costa Pacífica Colombiana. PhD thesis (in spanish), Universidad del Valle, Colombia.

55.

Pérez-Cruz

Urrutia-Fucugauchi

(2009) Magnetic mineral study of Holocene marine sediments from the Alfonso Basin, Gulf of California – Implications for depositional environment and sediment sources. Geofisica Internacional 48(3): 305–318.

56.

Porcasi

Fujita

(2011) Adaptation in the southern California Channel Islands. American Archaeology 65(3): 543–566.

57.

Prado-Ancona

(1998) Ciclo reproductivo de tres poblaciones de Chione californiensis Broderip, 1835 (Bivalvia: veneridae) poblaciones en Baja California Sur, México. PhD thesis (in spanish), Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, México.

58.

Ricaurte-Villota

González-Yajimovich

Sanchez

(2013) Coupled response of rainfall and denitrification to solar forcing during the Holocene in Alfonso Basin. Ciencias Marinas 39: 151–164.

59.

Rick

Kennett

Erlandson

(2004) Preliminary report on the archaeology and paleoecology of the Abalone Rocks Estuary, Santa Rosa Island, California. In: Garcelon

Schwemm

(eds) Proceedings of the sixth California Islands symposium, Ventura, California, USA, 1–3 December 2003, pp. 55–63. Institute for Wildlife Studies.

60.

Rick

Robbins

Ferguson

(2006) Stable isotopes from marine shells, ancient environments, and human subsistence on middle holocene santa rosa island, California, USA. The Journal of Island and Coastal Archaeology 1(2): 233–254.

61.

Robbins

(2006) Stable Isotopes, Marine Paleoclimates, and Human Subsistence on California’s Channel Islands. Dallas, TX: Southern Methodist University.

62.

Roland

Caseldine

Charman

, et al. (2014) Was there a “4.2 ka event” in Great Britain and Ireland? Evidence from the peatland record. Quaternary Science Reviews 83: 11–27.

63.

Rosales-López

Félix

García

, et al. (2003) Calculo de la biomasa marina del Conchalito. Estudios de Antropología Biológica XI: 871–909.

64.

Schöne

Rodland

Fiebig

, et al. (2006) Reliability of multitaxon, multiproxy reconstructions of environmental conditions from accretionary biogenic skeletons. The Journal of Geology 114(3): 267–285.

65.

Schöne

(2008) The curse of physiology—Challenges and opportunities in the interpretation of geochemical data from mollusk shells. Geo-Marine Letters 28(5–6): 269–285.

66.

Schöne

Flessa

Dettman

, et al. (2003) Upstream dams and downstream clams: Growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico). Estuarine, Coastal and Shelf Science 58(4): 715–726.

67.

Schöne

Gillikin

(2013) Unraveling environmental histories from skeletal diaries — Advances in sclerochronology. Palaeogeography Palaeoclimatology Palaeoecology 373: 1–5.

68.

Schrader

Pisias

Cheng

(1986) Seasonal variation of silicoflagellates in phytoplankton and varved sediments in the Gulf of California. Science 10: 207–233.

69.

Scroxton

Burns

McGee

, et al. (2020) Possible expression of the 4.2 kyr event in Madagascar and the south-east African monsoon. Climate of the Past Discussions. DOI: 10.5194/cp-2020-137.

70.

Staines-Urías

González-Yajimovich

Beaufort

(2015) Reconstruction of past climate variability and ENSO-like fluctuations in the southern Gulf of California (Alfonso Basin) since the last glacial maximum. Quaternary Research 83(3): 488–501.

71.

Wanner

Beer

Bütikofer

, et al. (2008) Mid- to late-Holocene climate change: An overview. Quaternary Science Reviews 27(19–20): 1791–1828.