Milankovitch frequencies in tephra records at volcanic arcs: The relation of kyr-scale cyclic variations in volcanism to global climate changes

Highlights The increase in volcanic activity after the last glacial maximum observed on Iceland has led to one of the most fascinating hypothesis in science in the last decades: that deglaciation may force volcanism. We: - Re-analyzed four longer tephra records with the same statistical method and demonstrated that all contain the ∼41 kyr and ∼100 kyr Millankovitch periodicities. - The frequency spectra of the tephra and δ18O records are significantly correlated supporting the hypothesis that orbital-driven global climate changes interact with the volcanic eruption frequency regionally and globally. - However, the simultaneous analysis of the four best-characterized tephra records shows that correlations and associated time lags suffer from a number of uncertainties including the nature and quality of tephra time series, a wide range in geographic latitudes and geological settings, as well as applied statistical methods Therefore more precise tephra time series (preservation and age optimized) from different regions (glaciated versus non-glaciated) and geological settings (island arcs, continental arcs, intraplate) are needed together with standardized statistical analysis to decipher the impact of these factors on a global perspective of how climate may control volcanism. Abstract The increase in volcanic activity after the last glacial maximum observed on Iceland has led to one of the most fascinating hypothesis in science in the last decades: that deglaciation may force volcanism. Consequently, tephrostratigraphic records of sufficient length that cover multiple glacial cycles have been used to test whether such relationships hold systematically through the Quaternary. Here we review such tephra records that have been linked with climate proxy records such as δ18O in marine sediments, which is a measure of sea-level change and which is thought to be orbitally forced, as it exhibits the characteristic Milankovitch periodicities of precession (∼23 kyr), obliquity (∼41 kyr) and eccentricity (∼100 kyr). Statistical analyses have identified these periodicities also in long tephra records from different latitudes and geotectonic settings, as well as in compiled semi-global records. These studies detect Milankovitch periods in their tephra record, and also a phase shift relative to the δ18O record in such that periods of increased eruption frequencies coincide with the deglaciation period at the glacial/interglacial transition when ice and water loads on the lithosphere change most rapidly. However, there are also disparities in results and interpretations, which may be attributable to the different methods of analysis applied by the studies. We have therefore re-analyzed the four best-characterized tephra records by the same methods. We distinguish between analysis in the frequency domain, a novel approach, and analysis in the time domain, which has been used in previous studies. Analysis in the frequency domain identifies harmonic frequencies that arise from the binary nature of the tephra records and complicate the identification of primary frequencies. However, we show that all four records show spectral density peaks near the main Milankovitch periodicities of 41 and 100 kyr, and that they produce meaningful and significant statistical correlations with each other and the global δ18O record but not with random time series. Although the time-domain correlations with δ18O roughly confirm phase shifts implying peak volcanism during deglaciation, correlation coefficients arising from very noisy records are generally too low for precise constraints on the relative timing. These deficiencies presently hamper the recognition of the physical mechanisms through which global climate changes affect volcanism at both, high-latitude glaciated regions and low-latitude non-glaciated regions

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

We examine the importance of dispersed volcanic ash as a critical component of the aluminosilicate sediment entering the Nankai Trough, located south of Japan’s island of Honshu, via the subducting Philippine Sea plate. Multivariate statistical analyses of an extensive major, trace, and rare earth element data set from bulk sediment and discrete ash layers at Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 quantitatively determine the abundance and accumulation of multiple aluminosilicate inputs to the Nankai subduction zone. We identify the eolian input of continental material to both sites, and we further find that there are an additional three ash sources from Kyushu and Honshu, Japan and other regions. Some of these ash sources may themselves represent mixtures of ash inputs, although the final compositions appear statistically distinct. The dispersed ash comprises 38 ± 7 weight percent (wt%) of the bulk sediment at Site C0011, and 34 ± 4 wt% at Site C0012. When considering the entire sediment thickness at Site C0011, the dispersed ash component supplies 38000 ± 7000 g/cm2 of material to the Nankai subduction system, whereas Site C0012 supplies 20000 ± 3000 g/cm2. These values are enormous compared to the ~2500 g/cm2 (C0011) and ~1200 g/cm2 (C0012) of ash in the discrete ash layers. Therefore, the mass of volcanic ash and chemically equivalent alteration products (e.g., smectite) that are dispersed throughout the stratigraphic succession of bulk sediment appears to be up to 15–17 times greater than the mass of discrete ash layers. The composition of the dispersed ash component at Site C0011 appears linked to that of the discrete layers, and the mass accumulation rate for dispersed ash correlates best with discrete ash layer thickness. In contrast, at Site C0012 the mass accumulation rate for dispersed ash correlates better with the number of ash layers. Together, the discrete ash layers, dispersed ash, and clay-mineral assemblages present a complete record of volcanism and erosion of volcanic sources; and indicate that mass balances and subduction factory budgets should include the mass of dispersed ash for a more accurate assessment of volcanic contributions to large-scale geochemical cycling

100- kyr cyclicity in volcanic ash emplacement: evidence from a 1.1 Myr tephra record from the NW Pacific

It is a longstanding observation that the frequency of volcanism periodically changes at times of global climate change. The existence of causal links between volcanism and Earth's climate remains highly controversial, partly because most related studies only cover one glacial cycle. Longer records are available from marine sediment profiles in which the distribution of tephras records frequency changes of explosive arc volcanism with high resolution and time precision. Here we show that tephras of IODP Hole U1437B (northwest Pacific) record a cyclicity of explosive volcanism within the last 1.1 Myr. A spectral analysis of the dataset yields a statistically significant spectral peak at the similar to 100 kyr period, which dominates the global climate cycles since the Middle Pleistocene. A time-domain analysis of the entire eruption and delta O-18 record of benthic foraminifera as climate/sea level proxy shows that volcanism peaks after the glacial maximum and similar to 13 +/- 2 kyr before the delta O-18 minimum right at the glacial/interglacial transition. The correlation is especially good for the last 0.7 Myr. For the period 0.7-1.1 Ma, during the Middle Pleistocene Transition (MPT), the correlation is weaker, since the 100 kyr periodicity in the delta O-18 record diminishes, while the tephra record maintains its strong 100 kyr periodicity

100- kyr cyclicity in volcanic ash emplacement: evidence from a 1.1 Myr tephra record from the NW Pacific

It is a longstanding observation that the frequency of volcanism periodically changes at times of global climate change. The existence of causal links between volcanism and Earth’s climate remains highly controversial, partly because most related studies only cover one glacial cycle. Longer records are available from marine sediment profiles in which the distribution of tephras records frequency changes of explosive arc volcanism with high resolution and time precision. Here we show that tephras of IODP Hole U1437B (northwest Pacific) record a cyclicity of explosive volcanism within the last 1.1 Myr. A spectral analysis of the dataset yields a statistically significant spectral peak at the ~100 kyr period, which dominates the global climate cycles since the Middle Pleistocene. A time-domain analysis of the entire eruption and δ18O record of benthic foraminifera as climate/sea level proxy shows that volcanism peaks after the glacial maximum and ∼13 ± 2 kyr before the δ18O minimum right at the glacial/interglacial transition. The correlation is especially good for the last 0.7 Myr. For the period 0.7–1.1 Ma, during the Middle Pleistocene Transition (MPT), the correlation is weaker, since the 100 kyr periodicity in the δ18O record diminishes, while the tephra record maintains its strong 100 kyr periodicity

Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment

Volcanic ash has long been recognized in marine sediment, and given the prevalence of oceanic and continental arc volcanism around the globe in regard to widespread transport of ash, its presence is nearly ubiquitous. However, the presence/absence of very fine-grained ash material, and identification of its composition in particular, is challenging given its broad classification as an “aluminosilicate” component in sediment. Given this challenge, many studies of ash have focused on discrete layers (that is, layers of ash that are of millimeter-to-centimeter or greater thickness, and their respective glass shards) found in sequences at a variety of locations and timescales and how to link their presence with a number of Earth processes. The ash that has been mixed into the bulk sediment, known as dispersed ash, has been relatively unstudied, yet represents a large fraction of the total ash in a given sequence. The application of a combined geochemical and statistical technique has allowed identification of this dispersed ash as part of the original ash contribution to the sediment. In this paper, we summarize the development of these geochemical/statistical techniques and provide case studies from the quantification of dispersed ash in the Caribbean Sea, equatorial Pacific Ocean, and northwest Pacific Ocean. These geochemical studies (and their sedimentological precursors of smear slides) collectively demonstrate that local and regional arc-related ash can be an important component of sedimentary sequences throughout large regions of the ocean

Data report: marine tephra compositions in the deep drilling cores of the South China Sea, IODP Expeditions 349 and 367/368

We present geochemical major and trace element glass data for tephra samples from International Ocean Discovery Program (IODP) Expeditions 349 and 367/368 from four drilling sites in the South China Sea. Overall, we obtained data for 55 samples and identified 46 as tephra layers, with dominant volcanic glass shards in the component inventory (in the 63–125 µ fraction). In total, we performed 720 single glass shard analyses using an electron microprobe for major element compositions, as well as 130 single glass shard analyses using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) for trace element compositions. The compositions of the samples range from basaltic, (trachy-) andesitic to trachytic, and rhyolitic and fall mainly into the calc-alkaline and K-rich calc-alkaline magmatic series. One sample falls into the shoshonitic series. Tephras from Expedition 349 Site U1431 span the whole compositional range, whereas tephras from the other sites are limited to rhyolitic composition. Tephra ages, calculated applying sedimentation rates, range to ~2 Ma at Site U1431, ~0.8 Ma at Expedition 367 Site U1499, ~0.6 Ma at Expedition 368 Site U1501, and ~0.9 Ma at Expedition 368 Site U1505

Miocene to Holocene marine tephrostratigraphy offshore northern Central America and southern Mexico: Pulsed activity of known volcanic complexes

We studied the tephra inventory of fourteen deep sea drill sites of three DSDP and ODP legs drilled offshore Guatemala and El Salvador (Legs 67, 84, 138), and one leg offshore Mexico (Leg 66). Marine tephra layers reach back from the Miocene to the Holocene. We identified 223 primary ash beds and correlated these between the drill sites, with regions along the volcanic arcs, and to specific eruptions known from land. In total, 24 correlations were established between marine tephra layers and to well‐known Quaternary eruptions from El Salvador and Guatemala. Additional 25 tephra layers were correlated between marine sites. Another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events. Tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites. Applying the respective sedimentation rates derived from the age models, we calculated ages for all marine ash beds. Hence, we also obtained new age estimates for eight known, but so far undated large terrestrial eruptions. Furthermore, this enables us to study the temporal evolution of explosive eruptions along the arc and we discovered five pulses of increased activity: 1) a pulse during the Quaternary, 2) a Pliocene pulse between 6 and 3 Ma, 3) a Late Miocene pulse between 10 and 7 Ma, 4) a Middle Miocene pulse between 17–11 Ma, and 5) an Early Miocene pulse (~>21 Ma)